<PAGE>   1
                                                                   EXHIBIT 10.35

                         BUILD TO SUIT OPTION AGREEMENT


        THIS BUILD TO SUIT OPTION AGREEMENT ("Agreement") is made and entered
into as of this 25th day of October, 1996, by and between MARTIN/CAMPUS
ASSOCIATES, L.P., a Delaware limited partnership ("Owner"), and AT HOME 
CORPORATION, a Delaware corporation ("AtHome").

                                R E C I T A L S

        This Agreement is made and entered into with reference to and upon the
basis of the following facts, intentions and understandings of the parties:

        A.      Owner is the owner of (a) that certain real property situated
in the City of Redwood City, County of San Mateo, State of California, which is
described on Exhibit A hereto (the "North Expansion Parcel"); provided, however,
that Owner holds an unconditional option to purchase, but does not own, the
so-called "Sears Parcel," as further described on Exhibit A-1 hereto (the "Sears
Parcel"); and (b) that certain unimproved real property situated in the City of
Redwood City, County of San Mateo, State of California, which is described on
Exhibit B hereto (the "South Expansion Parcel"). The North Expansion Parcel and
the South Expansion Parcel shall be hereinafter from time to time collectively
referred to as the "Property".

        B.      Owner and AtHome have entered into that certain Lease dated as
of October 18, 1996 (the "Broadway Lease") pursuant to which Owner is leasing to
AtHome, and AtHome is leasing from Owner, that certain real property commonly
known as 425 Broadway, situated in the City of Redwood City, County of San
Mateo, State of California (the "Broadway Premises").

        C.      As part of the consideration for the Broadway Lease, Owner
desires to give to AtHome, and AtHome desires to obtain from Owner, the option
to lease all or certain portions of the conditions, and the option to acquire a
portion of the Property on certain agreed terms and conditions.

        D.      Owner and AtHome now desire to enter into this Agreement to set
forth their agreement with respect to the above-described options and rights to
make a first offer.

        E.      All capitalized terms no specifically defined in this Agreement
shall have the same meanings given to them in the Broadway Lease.



                                       1
<PAGE>   2
        NOW, THEREFORE, in consideration of the payment by AtHome to Owner of
the sum of One Hundred Dollars ($100) and for other good and valuable
consideration, the receipt and adequacy of which are hereby acknowledged by
Owner, Owner and AtHome hereby agree as follows:

        1. Term. The term of this Agreement shall commence upon the execution 
of this Agreement by Owner and AtHome, and shall expire upon the expiration or 
earlier termination of this Agreement in accordance with the terms set forth 
below; provided, however, that if the First Option is not validly and timely 
exercised in accordance with the provisions of Paragraph 2.5, then the First 
Option, the Second Option, and the Third Option (all as defined below), and the 
option to purchase the Second Option Subparcel, shall immediately expire (if 
this Agreement has not already expired or been terminated) on the First Option 
Notice Date (as defined below), and this Agreement shall automatically 
terminate as of the First Option Notice Date; if the Second Option is not 
validly and timely exercised in accordance with the provisions of Paragraph 
2.6, then the Second Option and the Third Option, and the option to purchase 
the Second Option Subparcel, shall immediately expire (if this Agreement has 
not already expired or been terminated) on the Second Option Notice Date (as 
defined below); and if the Third Option is not validly and timely exercised in 
accordance with the provisions of Paragraph 2.7, then the Third Option shall 
immediately expire (if this Agreement has not already expired or been 
terminated) on the Third Option Notice Date (as defined below); and provided 
further, that if the owner of the Sears Parcel defaults under the option 
agreement with Owner for the Sears Parcel, this Agreement shall terminate with 
respect to the Sears Parcel. Notwithstanding the foregoing, if the owner of the 
Sears Parcel defaults under the option agreement with Owner for the Sears 
Parcel, and Owner nevertheless obtains title to the Sears Parcel, then so long 
as Owner and AtHome agree that it is feasible to do so, this agreement shall 
again apply to the Sears Parcel, with the same force and effect as if the 
Sears Parcel had always been part of the North Expansion Parcel; provided 
however, that the foregoing shall not be interpreted to require Owner to take 
any action to enforce the option agreement for the Sears Parcel, including 
without limitation commencing an action for specific performance of the option 
agreement.

                1.1 Other Documents. Upon expiration of the term of this 
Agreement with respect to any portion of the Property, or upon the expiration 
of the First Option, the Second Option, or the Third Option, AtHome shall 
execute, acknowledge and deliver to Owner an appropriate instrument prepared by 
Owner which Owner may then record in the Official Records of San Mateo County 
to expunge this Agreement and any memorandum thereof from the public record 
with respect to such portion of the Property. In addition, AtHome hereby 
irrevocably constitutes and appoints Owner as its true and lawful attorney in 
fact, in its name and in its behalf, to make, execute, acknowledge, deliver, 
and file any 

                                       2
<PAGE>   3
and all such instruments that AtHome so fails or refuses to execute. AtHome 
expressly understands and acknowledges that the foregoing special power of 
attorney is coupled with an interest, is irrevocable, and shall survive the 
dissolution or insolvency of AtHome, or the transfer by AtHome of the whole or 
any portion of its interest in this Agreement (provided that any such transfer 
shall be subject to the restrictions set forth in this Agreement).

        2.      AtHome's Options. AtHome shall have the option to lease certain 
property located in the Project on a build-to-suit basis (each, a "Build to 
Suit Option", and collectively, the "Build to Suit Options") on the terms and 
conditions described in this Agreement.

                2.1.    Option Deposit. AtHome shall, upon the execution of 
this Agreement by Owner and AtHome, deposit with Owner the sum of Five Hundred 
Thousand Dollars ($500,000.00) (the "Option Deposit"), as both consideration 
for Owner's willingness to grant the Build to Suit Options, and as security for 
AtHome performance of its obligations under the Build to Suit Options. As and 
when AtHome validly and timely exercises any of the Build to Suit Options in 
accordance with the provisions of this Agreement, Owner shall refund to AtHome 
that portion of the Option Deposit that equals Five Hundred Thousand Dollars 
($500,000.00) multiplied by a fraction, the numerator of which shall be the 
amount of square feet of Rentable Area to be located in the Proposed Building 
(as defined below) that is the subject of the Build to Suit Option then being 
exercised, and the denominator of which shall equal Four Hundred Ten Thousand 
(410,000); provided, however, that in no event shall AtHome be entitled to 
receive a refund in excess of the total remaining amount of the Option Deposit 
then being held by Owner; provided further, that if the total aggregate amount 
of Rentable Area approved by the City of Redwood City for the First Option 
Building, the Second Option Building and the Third Option Building (as those 
terms are defined below) is less than Four Hundred Ten Thousand (410,000) 
square feet, the denominator of such fraction shall equal the greater of (a) 
the total aggregate amount of Rentable Area approved by the City of Redwood 
City for the First Option Building, the Second Option Building and the Third 
Option Building, or (b) Three Hundred Eighty-Five Thousand (385,000) square 
feet. Notwithstanding anything to the contrary set forth above, in no event 
shall Owner be required to refund more than Five Hundred Thousand Dollars 
($500,000.00) to Tenant pursuant to this Paragraph 2. If AtHome fails to 
exercise any Build to Suit Option in accordance with the provisions of this 
Paragraph 2, or if any Build to Suit Option terminates as set forth in this 
Paragraph 2, then (i) AtHome shall immediately reimburse Owner for any and all 
costs, expenses and fees incurred by Owner to third parties in the process of 
carrying out any and all actions described or permitted under this Paragraph 2 
(including without limitation causing Architect to work on the conceptual 
plans, the Preliminary Plans and/or the Final Plans

                                       3
<PAGE>   4
(as those terms are defined below)), so long as such costs, expenses and fees 
have been approved as part of the budgeting process described in Paragraph 
2.1.1, and (ii) the entire remaining balance of the Option Deposit shall 
immediately become the property of Owner, and AtHome shall have no further 
right, title, claim, or interest in or to any portion of the Option Deposit. 
Owner shall not be required to segregate the Option Deposit from Owner's 
general funds; Owner's obligations with respect to the Option Deposit shall be 
those of a debtor and not a trustee, and AtHome shall not be entitled to any 
interest on the Option Deposit.

                  2.1.1. Approval of Budget. From time to time during the design
and planning process for the Proposed Buildings described in this Paragraph 2,
Owner shall present to AtHome a budget (each, a "Budget") showing in reasonable
detail the upcoming actions Owner intends to undertake pursuant to this
Paragraph 2, and the amount of costs, expenses and fees Owner estimates it will
incur to third parties in the course of carrying out such actions. AtHome shall
have ten (10) days after its receipt of any such Budget to review and approve
the same, provided that its approval of any such Budget shall not be
unreasonably withheld. If AtHome disapproves any matter or line item contained
in such Budget, then Owner may at its election either submit a revised Budget
for AtHome's review and approval (in which event AtHome and Owner shall continue
to follow the procedures set forth in this Paragraph 2.1.2), or proceed with the
actions described in the originally submitted Budget without obtaining AtHome's
approval thereof. If AtHome neither approves nor disapproves the Budget within
such 10-day period, AtHome shall be deemed to have approved such Budget as
submitted. 

                  2.2. Architect. Within a reasonable period of time after the
execution of this Agreement, Owner shall notify AtHome in writing of the name
and address of the licensed architect whom Owner desires to engage for the
preparation of conceptual designs for the Expansion Project (as defined below).
Owner's architect ("Architect") shall be subject to AtHome's prior written
approval, which approval shall not be unreasonably withheld or delayed. Owner
shall not replace the Architect without obtaining AtHome's prior written
approval, which approval shall not be unreasonably withheld or delayed. For the
purposes of this Agreement, the term "Expansion Project" shall mean the Proposed
Buildings consisting of approximately Four Hundred Ten Thousand (410,000) square
feet of Rentable Area that Owner may develop for AtHome on the North Expansion
Parcel and the South Expansion Parcel under the Build to Suit Options; and the
term "Proposed Building" shall mean the building or buildings to be constructed
pursuant to any Build to Suit Option.

                  2.2.1. Initial Design Process. Commencing between January 1, 
1997 and March 31, 1997, Owner and AtHome shall work with Architect to develop 
conceptual designs for the Expansion Project consistent with those certain 
plans prepared by 

                                       4
<PAGE>   5


Ken Rodriguez, copies of which are attached hereto as Exhibit F (the "Basic Site
Plans"). The conceptual designs shall set forth, without limitation, the size,
elevations, locations, and proposed phasing for the development of the Proposed
Buildings to be included in the Expansion Project; schematic plans for the
Proposed Buildings; and design development information sufficient to enable the
parties to obtain preliminary pricing from Contractor (as defined below) for the
construction of the Proposed Building. The parties acknowledge and agree that
the size and location of the Proposed Building to be constructed under each of
the Build to Suit Options, and the proposed phasing for the development of the
Proposed Buildings, is of critical importance under this Agreement, and AtHome
agrees to provide the proposed size ad location of such Proposed Building, and
the proposed phasing for the development of the Proposed Buildings, as early in
the process described in this Paragraph 2.2.1 as shall be feasibly possible. The
size of each Proposed Building shall be subject to the minimum sizes set forth
in Paragraphs 2.5, 2.6 and 2.7; the size and location of each Proposed Building
shall be subject to the reasonable approval of Owner; and the phasing for the
development of the Proposed Buildings shall be subject to the approval of Owner,
which may be withheld in Owner's sole discretion. Owner shall have no right to
disapprove the size or location of any Proposed Building to the extent that the
size or location proposed by AtHome is consistent with the Basic Site Plans.
Each Proposed Building shall at a minimum be designed to the following standard
(the "Minimum Building Standard"): a multi-story steel-framed structure suitable
for office use, with a glass and drivet exterior. For the purposes of this
Agreement, the "phasing" for the development of the Proposed Buildings shall
mean the timing for the development of the First Option Building, the Second
Option Building, and the Third Option Building, and the areas within the
Property where the First Option Building, the Second Option Building, and the
Third Option Building shall be located; and the "location" of a Proposed
Building shall mean the placement and alignment of the footprint of such
Proposed Building within the building area described in the phasing for the
development of the Proposed Buildings.

                      2.2.2.   Conceptual Designs. Based on the information
provided by AtHome as described above, Owner shall cause Architect to prepare
conceptual designs for the Expansion Project consistent with the Basic Site
Plans, and shall provide AtHome with copies of and the opportunity to comment
upon, all drafts of such conceptual designs. To the extent that AtHome offers
specific written comments to any such designs, and such comments are reasonably
acceptable to Owner, Owner shall use reasonable efforts to cause Architect to
consider such comments and/or incorporate such comments into a revised draft of
such designs. The collaborative process described in this Paragraph 2.2 shall
continue until the first to occur of (a) August 31, 1997, or (b) such time as
Owner and AtHome reach agreement upon the conceptual designs for the Expansion
Project. However, if


                                       5
<PAGE>   6
Owner and AtHome fail to agree upon such conceptual designs by August 31, 1997, 
then Owner shall cause Architect to prepare and submit to AtHome on or before 
September 30, 1997, and AtHome shall be deemed to have approved, a conceptual 
design ("Landlord's Conceptual Design") for the Expansion Project consistent 
with the Basic Site Plans that calls for each of the Proposed Buildings to be 
constructed to the Minimum Building Standard. Landlord's Conceptual Design 
shall reflect Owner's reasonable determination of the size and location of the 
Proposed Buildings (so long as such size and location is consistent with the 
Basic Site Plans), and the schematic plans and design development information 
for the Proposed Buildings, all taking into consideration the standards set 
forth in this Agreement and the information and requests submitted by Tenant. 
The conceptual designs for the Proposed Buildings prepared pursuant to this 
Paragraph 2.2.2, whether agreed upon by Owner and AtHome, or prepared as 
Landlord's Conceptual Design by Architect at Owner's request, shall hereafter 
be collectively called the "Approved Conceptual Designs".

        2.3.  Build to Suit Notice.  In order to elect to exercise any of the 
Build to Suit Options, AtHome shall deliver to Owner, on or before the 
applicable Option Notice Date (as defined below), a written notice (with each 
such notice being called a "Build to Suit Notice") setting forth AtHome's 
exercise of the Build to Suit Option, and identifying the Proposed Building to 
which such Build to Suit Notice applies, the proposed size and location of the 
Proposed Building, and the proposed phasing for the development of the Proposed 
Buildings. The size and location of the Proposed Building shall be subject to 
the reasonable approval of Owner; and the phasing for the development of the 
Proposed Buildings shall be subject to the approval of Owner, which may be 
withheld in Owner's sole discretion. Owner shall have no right to disapprove 
the size or location of any Proposed Building to the extent that the size or 
location proposed by AtHome is consistent with the Basic Site Plans. The Build 
to Suit Notice must be accompanied by (i) two copies of a Lease identical to 
the form of the Lease attached hereto as Exhibit C, executed by AtHome and with 
all blanks filled in with appropriate information satisfactory to Landlord, and 
(ii) AtHome's check payable to Owner in an amount equal to the aggregate of the 
advance payment of monthly rent set forth in the second grammatical paragraph 
of Paragraph 5.A of the Lease, and the security deposit set forth in Paragraph 
6 of the Lease. The parties acknowledge and agree that the process described in 
this Paragraph 2.3 is only intended to apply to the construction of the Shell 
and Core of each Proposed Building (as those terms are defined in Exhibit D 
attached hereto), and that the design and planning of the tenant improvements 
for each Proposed Building will be handled in the manner set forth in the work 
letter to be attached to each respective Lease for a Proposed Building.

                2.3.1.  Preliminary Plans.  Owner shall cause Architect to 
prepare preliminary plans (the "Preliminary Plans")

                                       6
<PAGE>   7


for the Proposed Building, based upon the Approved Conceptual Designs. Owner
shall use reasonable efforts to cause Architect to deliver the Preliminary Plans
to AtHome within fifteen (15) days after Owner's receipt of the Build to Suit
Notice for such Proposed Building; provided, however, that Owner may in its sole
discretion elect to cause Architect to commence preparing the Preliminary Plans
prior to completion of the Approved Conceptual Designs. Within five (5) days
after AtHome's receipt of the Preliminary Plans, AtHome shall either approve or
disapprove the Preliminary Plans. If AtHome disapproves the Preliminary Plans,
then AtHome shall state in reasonable detail the changes which AtHome requires
to be made thereto. Owner shall use reasonable efforts to cause Architect to
submit to AtHome revised Preliminary Plans within five (5) days after Owner's
receipt of AtHome's disapproval notice. Following AtHome's receipt of the
revised Preliminary Plans from Owner, AtHome shall have the right to review and
approve the revised Preliminary Plans pursuant to this Paragraph 2.3.1. AtHome
shall give Owner written notice of its approval or disapproval of the revised
Preliminary Plans within five (5) days after the date of AtHome's receipt
thereof. If AtHome disapproves the revised Preliminary Plans, then AtHome and
Owner shall continue to follow the procedures set forth in this Paragraph 2.3.1
until either (a) AtHome and Owner approve the Preliminary Plans in accordance
with this Paragraph 2.3.1, or (b) the date that is thirty (30) days after
Owner's receipt of the Build to Suit Notice, whichever shall first occur. If
AtHome and Owner do not mutually agree upon the Preliminary Plans within such
30-day period, then AtHome may, in its sole discretion, elect by written notice
(the "Preliminary Plan Acceptance Notice") delivered to Owner within three (3)
days after AtHome's receipt of written notice from Owner that such 30-day period
has expired (and Owner shall have the right to deliver such notice to AtHome as
early as three (3) days before the expiration of such 30-day period), to either
(i) accept the last version of the Preliminary Plans submitted by Owner to
AtHome pursuant to this Paragraph 2.3.1, or (ii) agree that Architect shall
prepare an initial version of the Final Plans (as defined below) for the
Proposed Building based upon the Minimum Building Standard, and that no
Preliminary Plans are required under this Paragraph 2.3.1. If AtHome and Owner
do not mutually agree upon the Preliminary Plans within the 30-day period
described above, and AtHome does not deliver the Preliminary Plan Acceptance
Notice to Owner within the 3-day period described above, then such Build to Suit
Option and all unexercised Build to Suit Options shall terminate and cease to be
of any force or effect, effective upon the expiration of such 30-day period. If
AtHome neither approves nor disapproves the Preliminary Plans or the revised
Preliminary Plans within the applicable time periods provided above, AtHome
shall be deemed to have disapproved such Preliminary Plans as submitted.

        2.3.2.  Final Plans.    Owner shall use reasonable efforts to cause
Architect to deliver to AtHome, within ten (10) days after approval by AtHome
and Owner of the



                                       7
<PAGE>   8
Preliminary Plans, complete plans and specifications which incorporate and are
consistent with the approved Preliminary Plans, and which show in detail the
intended design, construction and finishing of all portions of the Proposed
Building (the "Final Plans"). Within five (5) days after AtHome's receipt of the
Final Plans, AtHome shall either approve or disapprove the Final Plans. If
AtHome disapproves the Final Plans, then AtHome shall state in reasonable detail
the changes which AtHome requires to be made thereto. Owner shall use reasonable
efforts to cause Architect to submit to AtHome revised Final Plans within five
(5) days after Owner's receipt of AtHome's disapproval notice. Following
AtHome's receipt of the revised Final Plans from Owner, AtHome shall have the
right to review and approve the revised Final Plans pursuant to this Paragraph
2.3.2. AtHome shall give Owner written notice of its approval or disapproval of
the revised Final Plans within five (5) days after the date of AtHome's receipt
thereof. If AtHome disapproves the revised Final Plans, then AtHome and Owner
shall continue to follow the procedures set forth in this Paragraph 2.3.2 until
either (a) AtHome and Owner approve such Final Plans in accordance with this
Paragraph 2.3.2, or (b) the date that is sixty (60) days after Owner's receipt
of the Build to Suit Notice. If AtHome and Owner do not mutually agree upon the
Final Plans within such 60-day period, then AtHome may, in its sole discretion,
elect by written notice (the "Final Plan Acceptance Notice") delivered to Owner
within three (3) days after AtHome's receipt of written notice from Owner that
such 60-day period has expired (and Owner shall have the right to deliver such
notice to AtHome as early as three (3) days before the expiration of such 60-day
period), to either (i) accept the last version of the Final Plans submitted by
Owner to AtHome pursuant to this Paragraph 2.3.2, or (ii) agree that Owner may
proceed with the construction of the Proposed Building by utilizing plans and
specifications to be prepared by Architect based upon the Minimum Building
Standard, that AtHome shall have no right to approve or reject such plans and
specifications, and that such plans and specifications shall be deemed to
constitute the "Final Plans" for the purposes of this Agreement. If AtHome and
Owner do not mutually agree upon the Final Plans within the 60-day period
described above, and AtHome does not deliver the Final Plan Acceptance Notice to
Owner within the 3-day period described above, then such Build to Suit Option
and all unexercised Build to Suit Options shall terminate and cease to be of any
force or effect, effective upon the expiration of such 60-day period. If AtHome
neither approves nor disapproves the Final Plans within the applicable time
periods provided above, AtHome shall be deemed to have disapproved the Final
Plans as submitted.

                        2.3.3   Construction Budget. Owner intends to retain 
Devcon Construction ("Contractor" as the general contractor for the 
construction of the Proposed Buildings. AtHome shall have the right to approve 
the construction contract between Owner and Contractor for the construction of 
any Proposed Building, which approval shall not be unreasonably withheld or 
delayed; provided, however, that AtHome shall have no right to

                                       8
<PAGE>   9
disapprove such construction contract if such construction contract conforms in 
all material respects with the applicable AIA form contract and general 
conditions. Owner shall have the right to replace the Contractor at any time, 
provided that any other contractor proposed by Owner shall not be designated as 
the "Contractor" under this Agreement without AtHome's prior written approval, 
which approval shall not be unreasonably withheld or delayed. Upon approval by 
Owner and AtHome of the Final Plans, Owner shall instruct Contractor to obtain 
competitive bids for the Proposed Building from at least three (3) qualified 
subcontractors for each of the major subtrades (excluding the mechanical and 
electrical trades, which shall be on a design/build basis; provided, however, 
that Owner shall review the proposed costs of such design/build mechanical and 
electrical work, and use reasonable efforts to keep the overall costs of such 
design/build mechanical and electrical work at commercially reasonable levels), 
and to submit the same to Owner and AtHome for their review and approval. Upon 
selection of the subcontractors and approval of the bids, Contractor shall 
prepare a cost estimate for the Proposed Building described in such Final 
Plans, based upon the bids submitted by the subcontractors selected. Contractor 
shall submit such cost estimate to Owner and AtHome for their review and 
approval, based upon the terms set forth in Paragraph 2 of Exhibit D hereto. 
Owner and AtHome may reject such cost estimate only if (a) those Development 
Costs (as defined in Exhibit D) described in Paragraph 2.2 of Exhibit D hereto 
exceed the Adjustable Cost Limit (as defined in Exhibit D), or (b) the annual 
rent for the Proposed Building will be less than the minimum return described 
in Paragraph 2.2 of Exhibit D hereto, and AtHome does not agree to increase the 
rent payable under that Build to Suit Lease pursuant to Paragraph 2.3 of 
Exhibit D hereto. If either Owner or AtHome rejects such cost estimate in 
accordance with this Paragraph 2.3.3, and Owner and AtHome fail to agree on 
revisions to the Final Plans within ten (10) days after their receipt of the 
cost estimate, then such Build to Suit Option shall terminate and cease to be 
of any force or effect in accordance with Paragraph 2.3 of Exhibit D hereto, 
and all unexercised Build to Suit Options shall also terminate effective upon 
the termination of such Build to Suit Option. Following any submission of 
revised Final Plans to Contractor and a resolicitation of bids by Contractor, 
Owner and AtHome shall again follow the procedures set forth in this Paragraph 
2.3.3 with respect to the submission and approval of the cost estimate from 
Contractor until either (i) Owner and AtHome approve such cost estimate in 
accordance with this Paragraph 2.3.3, or (ii) the date that is ninety (90) days 
after Owner's receipt of AtHome's Build to Suit Notice. If Owner and AtHome do 
not mutually agree upon the cost estimate within such 90-day period, and AtHome 
does not agree to increase the rent payable under that Build to Suit Lease 
pursuant to Paragraph 2.3 of Exhibit D hereto, then such Build to Suit Option 
and all unexercised Build to Suit Options shall terminate and cease to be of 
any force or effect in accordance with Paragraph 2.3 of Exhibit D hereto, and 
all unexercised Build to Suit Options shall also terminate 

                                       9
<PAGE>   10
effective upon the termination of such Build to Suit Option. If either Owner or
AtHome neither approves nor disapproves the cost estimate within the applicable
time periods provided above, such party shall be deemed to have disapproved the
cost estimate as submitted.

                2.3.4.  Construction Financing. If Owner and AtHome have both
accepted Contractor's cost estimate for the Proposed Building pursuant to
Paragraph 2.3.3 above, Owner shall have a period of thirty (30) days after such
mutual acceptance of the cost estimate to use reasonable efforts to attempt to
obtain a loan for the costs of constructing the Proposed Building ("Construction
Financing"), in an amount not less than the total amount of estimated
Development Costs (as defined in Paragraph 1 of Exhibit D hereto), less the Land
Value (as defined in Paragraph 1.1 of Exhibit D hereto), under such commercially
reasonable terms and conditions as shall be reasonably acceptable to Owner
(including, if necessary, a commercially reasonable completion guaranty provided
by Owner); provided, however, that in no event shall Owner be required to
provide any other form of credit enhancement or any third party guaranty as
security for such Construction Financing, including without limitation any
guaranty from the partners or members of Owner. If Owner is unable to obtain
Construction Financing under such commercially reasonable terms, Owner may, by
giving written notice to AtHome within such 30-day period, elect to terminate
its obligation to construct such Proposed Building, in which event such Build to
Suit Option and all unexercised Build to Suit Options shall terminate and cease
to be of any force or effect, effective upon the expiration of such 30-day
period; provided, however, that if within such 30-day period AtHome delivers
written notice to Owner whereby AtHome covenants and agrees to provide the
"AtHome Loan" (as defined below) to Owner to finance the cost of constructing
the Proposed Building, and AtHome funds the AtHome Loan in accordance with the
following terms and conditions, then such Build to Suit Option and all
unexercised Build to Suit Options shall remain in full force and effect. The
AtHome Loan shall be interest-free; in an amount not less than the total amount
of estimated Development Costs less the Land Value; and for a term, with a
funding schedule, and on such other terms and conditions as shall be
commercially reasonable, as reasonably determined by Owner (including, if
necessary, a commercially reasonable completion guaranty provided by Owner);
provided, however, that in no event shall Owner be required to provide any other
form of credit enhancement or any third party guaranty as security for the
AtHome Loan. The AtHome Loan shall be evidenced by such commercially reasonable
loan documents as shall be mutually acceptable to Owner and AtHome.

                2.4.    Agreement as to Terms. Should the parties reach
agreement on the location and design of the Proposed Building and the cost and
schedule for the construction of the Proposed Building within the applicable
time periods described in this Paragraph 2, such agreement shall be evidenced by
a written 


                                       10
<PAGE>   11


lease agreement (each, a "Build to Suit Lease") in substantially the form of the
Lease attached hereto as Exhibit C, but containing (a) the terms and conditions
to which Owner and AtHome have specifically agreed pursuant to this Paragraph 2
(the "Specific Terms"), and (b) the terms and conditions set forth on Exhibit D
attached to this Agreement (the "General Terms"). To the extent there is any
discrepancy between the Specific Terms and the General Terms, the Specific Terms
shall be controlling.

               2.5.    First Option. AtHome shall have until September 30, 1997
(the "First Option Notice Date") to deliver to Owner AtHome's first Build to
Suit Notice (the "First Option"); provided, however, that AtHome shall not be
entitled to exercise the First Option unless and until AtHome has either (a)
both (i) raised at least Thirty-Five Million Dollars ($35,000,000.00) in
additional equity funds (over and above those equity funds raised by AtHome on
or prior to the date the Broadway Lease is executed by Owner and AtHome), and
(ii) demonstrated to Owner's reasonable satisfaction that AtHome's assets
include currently available funds equal to least Thirty-Five Million Dollars
($35,000,000.00), or (b) completed an initial public offering of its common
stock on a national stock exchange or on an over-the-counter basis. The failure
of AtHome so to exercise the First Option on or before the First Option Notice
Date shall terminate AtHome's rights to exercise the First Option and all other
Build to Suit Options. If AtHome validly and timely exercises that First Option
in accordance with this Paragraph 2.5, the Second Option and the Third Option
shall remain in full force and effect. The Proposed Building(s) under the First
Option (which may be made up of two separate buildings) (collectively, the
"First Option Building") shall contain a minimum Rentable Area of not less than
One Hundred Fifty Thousand square feet (150,000); provided, however, that if at
the time AtHome exercises the First Option, AtHome has previously exercised its
option to lease the entire building within the Project commonly known as 2945
Bay Road (the "Bay Road Premises"), the minimum Rentable Area of the First
Option Building would be One Hundred Fifty Thousand (150,000) square feet minus
the Rentable Area of the Bay Road Premises.

               2.6.    Second Option. If AtHome exercises the First Option in
accordance with Paragraph 2.5, and Owner and AtHome execute a Build to Suit
Lease with respect to the First Option, then AtHome shall have until March 30,
1998 (the "Second Option Notice Date") to deliver to Owner AtHome's second Build
to Suit Notice (the "Second Option"); provided, however, that AtHome shall not
be entitled to exercise the Second Option unless and until AtHome has completed
an initial public offering of its common stock on a national stock exchange or
on an over-the-counter basis. The failure of AtHome so to exercise the Second
Option on or before the Second Option Notice Date shall terminate AtHome's
rights to exercise the Second Option and the Third Option, and shall terminate
AtHome's right to exercise its option to purchase the Second Option Subparcel
(as defined below) 


                                       11
<PAGE>   12
pursuant to Paragraph 3. If AtHome validly and timely exercises the Second 
Option in accordance with this Paragraph 2.6, the Third Option shall remain in 
full force and effect. The Proposed Building under the Second Option (which may 
be made up of two (2) separate buildings) (collectively, the "Second Option 
Building") shall contain a minimum Rentable Area of not less than One Hundred 
Fifty Thousand (150,000) square feet; provided, however, that if at the time 
AtHome exercises the Second Option, AtHome has previously leased the Bay Road 
Premises and the First Option Building, the minimum Rentable Area of the Second 
Option Building would be reduced by the extent to which (a) the sum of the 
Rentable Area of the Bay Road Premises, and the Rentable Area of the First 
Option Building, exceeds (b) One Hundred Fifty Thousand (150,000) square feet.

                2.7.  Third Option.  If AtHome exercises the First Option and 
the Second Option in accordance with Paragraphs 2.5 and 2.6, and Owner and 
AtHome have executed Build to Suit Leases with respect to the First Option and 
the Second Option, then AtHome shall have until December 31, 1998 (the "Third 
Option Notice Date") to deliver to Owner the third Build to Suit Notice (the 
"Third Option"). The failure of AtHome so to exercise the Third Option on or 
before the Third Option Notice Date shall terminate AtHome's right to exercise 
the Third Option. The failure of AtHome so to exercise the Third Option on or 
before the Third Option Notice Date shall terminate AtHome's rights to exercise 
the Third Option. The Proposed Building under the Third Option (the "Third 
Option Building") shall consist of the entire amount of remaining entitled 
office space situated in the South Expansion Parcel, and the North Expansion 
Parcel. The First Option Notice Date, the Second Option Notice Date, and the 
Third Option Notice Date shall be collectively called the "Option Notice Dates".

                2.8.  Conditions to Exercise.  The effectiveness of AtHome's 
right to exercise the Build to Suit Options, as set forth in this Paragraph 2, 
is in each instance conditioned on the following: (a) AtHome has not previously 
entered into a Sublet of any Build to Suit Lease or the Broadway Lease (other 
than a Permitted Transfer); and (b) no monetary or other default by AtHome 
exists under the Broadway Lease which remains uncured after the giving of any 
applicable notice and the expiration of any applicable cure period. In 
addition, if any of the conditions specified under clauses (a) or (b) above do 
not continue to be satisfied as of the date on which the Build to Suit Lease is 
to commence, then unless Owner waives in writing any of such conditions, 
AtHome's exercise of the Build to Suit Option under this Paragraph 2 shall be 
null and void, and this Agreement and the Build to Suit Lease shall terminate 
effective as of the date on which the Build to Suit Lease was to commence.

                                       12
<PAGE>   13
        3. Option to Purchase.

                3.1 Option to Purchase Second Option Subparcel. Owner shall use
reasonable efforts to subdivide the property on which the Second Option Building
is to be situated so that one of the buildings comprising the Second Option
Building becomes situated on one or more legal parcels (which parcel or parcels,
together with all rights and appurtenances thereto, are collectively called the
"Second Option Subparcel"), separate and apart from any other areas of the
Project and the North Expansion Parcel. If Owner so creates the Second Option
Subparcel in a configuration acceptable to Owner, then upon AtHome's exercise of
the Second Option in accordance with the requirements set forth in Paragraph 2.3
above, AtHome shall have the option to (in lieu of requiring Owner to develop
the Second Option Building to be situated on the Second Option Subparcel)
acquire, on an all cash basis, in the manner set forth in Paragraph 3.2, fee
title to the Second Option Subparcel, so long as the Second Option Subparcel is,
in Owner's judgment, of sufficient size and has been granted sufficient
entitlements to develop a building containing at least Seventy-Five Thousand
(75,000) square feet of Rentable Area. The purchase price for the Second Option
Subparcel shall be equal to the product of Sixty-Five and 25/100ths Dollars
($65.25) multiplied by the total amount of square feet of Rentable Area approved
by the City of Redwood City for the Second Option Building to be constructed on
the Second Option Subparcel, but in no event shall the purchase price be less
than Four Million Eight Hundred Ninety-Three Thousand Seven Hundred Fifty
Dollars ($4,893,750.00). In order to elect to exercise its option to acquire the
Second Option Subparcel, AtHome shall deliver to Owner, concurrently with its
delivery to Owner of AtHome's notice exercising the Second Option, a written
notice setting forth AtHome's exercise of its option to acquire the Second
Option Subparcel (the "Second Option Subparcel Notice"). The Second Option
Subparcel Notice shall not be effective unless it includes the following: (i)
immediately available funds in an amount equal to five percent (5%) of the
purchase price for the Second Option Subparcel (the "Deposit"), and (ii)
AtHome's execution of the liquidated damage provision set forth in Exhibit E
attached to this Agreement. The Deposit shall be held by the Title Company,
defined in Exhibit E, in an interest bearing account and shall constitute
liquidated damages, and shall be paid to Owner in the event AtHome fails to
consummate the purchase of the Second Option subparcel in accordance with the
terms of this Paragraph 3, other than as a direct result of Owner's failure to
perform its obligations under this Paragraph 3 or Exhibit E. Escrow for the sale
of the Second Option Subparcel to AtHome shall close thirty (30) days after
Owner's receipt of the Second Option Subparcel Notice, or such other date as
Owner and AtHome shall mutually agree. AtHome's acquisition of the Second Option
Subparcel shall be subject to the provisions of Paragraphs 3.2. If AtHome does
not deliver the Second Option Subparcel Notice to Owner as described above, then
AtHome's option to purchase the Second Option Subparcel shall terminate and
cease to be of any

                                       13
<PAGE>   14
force or effect as of the Second Option Notice Date. All closing, title 
insurance and transfer costs, including without limitation applicable sales and 
transfer taxes, associated with AtHome's acquisition of the Second Option 
Subparcel shall be paid by Owner and AtHome in accordance with the custom in 
San Mateo County.

                        3.1.1.  Effect of Exercise. Notwithstanding anything to 
the contrary set forth in Paragraph 3.1 above, AtHome's exercise of its option 
to acquire the Second Option Subparcel pursuant to Paragraph 3.1 shall have no 
affect upon AtHome's right and obligation to lease the balance of the Second 
Option Building in accordance with the terms and conditions set forth in 
Paragraph 2; provided, however, that such terms and conditions shall be 
equitably adjusted as may be reasonably necessary in order to account for the 
fact that AtHome is purchasing rather than leasing the Second Option Subparcel.

                3.2     Conditions. The effectiveness of AtHome's option to 
acquire the Second Option Subparcel, as set forth in this Paragraph 3, is 
conditioned on the following: (a) AtHome has not previously entered into a 
Sublet of any Build to Suit Lease or the Broadway Lease that requires Owner's 
consent; and (b) no monetary or other material default by AtHome exists under 
either any Build to Suit Lease or the Broadway Lease which remains uncured 
after the giving of any applicable notice and the expiration of any applicable 
cure period. In addition, if any of the conditions specified under clauses (a) 
or (b) above do not continue to be satisfied as of the date on which the escrow 
for the sale of the Second Option Subparcel to AtHome is scheduled to close, 
then unless Owner waives in writing any such conditions, AtHome's exercise of 
its right to acquire the Second Option Subparcel under this Paragraph 3 shall 
be null and void, and this Agreement shall terminate effective as of the date 
on which the escrow for the sale of the Second Option Subparcel to AtHome was 
scheduled to close.

                3.3     Process. Should AtHome exercise its option to acquire 
the Second Option Subparcel within the applicable period of time set forth in 
this Paragraph 3, AtHome's acquisition of the Second Option Subparcel shall be 
carried out on (a) the terms and conditions described in this Paragraph 3 (the 
"Agreed Second Option Subparcel Terms"), and (b) the terms and conditions set 
forth on Exhibit E attached to this Agreement (the "Standard Terms"). To the 
extent there is any discrepancy between the Agreed Terms and the Standard 
Terms, the Agreed Terms shall be controlling.

        4.      Rights Personal. The options granted to AtHome under Paragraphs 
2 and 3 shall all be personal to AtHome, and shall not be assigned, sold, 
conveyed or otherwise transferred to any other party (including without 
limitation any assignee or sublessee of such AtHome) without the prior written 
consent of Owner, which consent may be withheld in Owner's sole discretion;

                                       14
<PAGE>   15
provided, however, that the rights granted to AtHome under Paragraph 3 without 
Owner's consent may be transferred to the transferee of AtHome's interest in 
the Broadway Lease pursuant to a Permitted Transfer. For the purposes of this 
Agreement, the term "AtHome" shall be deemed to include any such transferee to 
whom AtHome has assigned its rights under Paragraph 3. 

                  5.  Events Of Default And Remedies Upon Default.

                      5.1. Events of Default. The occurrence of any of the 
following, whatever the reason therefor, shall constitute an "Event of Default" 
by AtHome under this Agreement:

                      (a) AtHome fails to perform or observe any of its 
obligations under this Agreement; or
                       
                      (b) AtHome fails to cure within any applicable grace 
period any default by AtHome or any of its Affiliates under any other agreement 
by and between Owner (or Owner's successors and assigns) and AtHome, or their 
respective Affiliates, including without limitation each Build to Suit Lease, 
the Broadway Lease, that certain Agreement Granting Right of First Offer of 
even date herewith ("First Offer Agreement"), and that certain Option Agreement 
(Bay Road) of even date herewith ("Bay Road Option"), and any and all leases 
entered into by and between Owner and AtHome, or their respective Affiliates, 
pursuant to the First Offer Agreement or the Bay Road Option (collectively, the 
"Other Documents").

                       5.2. Remedies Upon Default. Upon the occurrence of any
Event of Default, Owner may, at its option terminate this Agreement by
delivering written notice of such termination to AtHome, in which event Owner
shall, as of the date of delivery of such notice, be free to enter into a lease
with a third party or parties for all or any portion of the Property (separately
or together with any other premises) upon any terms whatsoever. The provisions
of this Paragraph 5 shall have no effect upon Owner's ability to exercise any
and all of its rights under the Other Documents.

                  6. Brokers. Owner and AtHome acknowledge and agree that 
certain real estate brokers (including without limitation Colliers Parrish 
International, AMB Corporate Real Estate Advisors and BT Commercial) have been 
involved in the Broadway Lease. AtHome warrants and represents that it has had 
no dealings with any other real estate broker or agent in connection with the 
negotiation of this Agreement, and that it knows of no other real estate broker 
or agent who is or might be entitled to a commission in connection with this 
Agreement. AtHome shall indemnify, defend and hold Owner harmless from and 
against any and all claims, causes of action, liability or costs, including 
reasonable attorney's fees, arising as a result of a breach of the foregoing 
warranty and representation. Nothing contained in


                                       15
<PAGE>   16
this Paragraph 6 shall be deemed to obligate or require Owner to pay any
commission whatsoever to any real estate broker __________ (including without
limitation Colliers Parrish International, AMB Corporate Real Estate Advisors
and BT Commercial) with respect to this Agreement; the payment of any such
commission (if any) shall be governed by a separate written agreement between
Owner and the real estate broker or brokers in question.

        7.      Notices. The address of each party for the purpose of all
notices permitted or required by this Agreement is as follows:

        To Owner:       Martin/Campus Associates, L.P.
                        100 Bush Street
                        San Francisco, CA 94104
                        Attn: Cathy Greenwold

        To AtHome:      At Home Corporation
                        385 Ravendale Drive
                        Mountain View, CA 94043
                        Attn: Ken Goldman

        Any notice or demand required or desired to be given under this
Agreement shall be in writing and shall be personally served or in lieu of
personal service may be given by certified mail, facsimile, or overnight courier
service. All notices or demands under this Agreement shall be deemed given,
received, made or communicated on the date personal delivery is effected; or, if
sent by certified mail, on the delivery date or attempted delivery date shown on
the return receipt; or, if sent by facsimile, on the date sent by the sender;
or, if sent by overnight courier service, on the delivery date or attempted
delivery date shown on such service's records. Either party may change its
address by giving notice of same in accordance with this Paragraph 7.

        8.      Captions. The captions and headings used in this Agreement are
for the purpose of convenience only and shall not be construed to limit or
extend the meaning of any part of this Agreement.

        9.      Executed Copy. Any fully executed copy of this Agreement shall
be deemed an original for all purposes.

        10.     Time.   Time is of the essence for the performance of each term,
condition and covenant of this Agreement.

        11.     Separability. If one or more of the provisions contained herein,
is for any reason held invalid, illegal or unenforceable in any respect, such
invalidity, illegality, or unenforceability shall not affect any other
provision of this Agreement, but this Agreement shall be construed as if such



                                       16
<PAGE>   17
invalid, illegal or unenforceable provision had not been contained herein.

     12.  Choice of Law. This Agreement and the rights and obligations of the 
parties hereunder shall be construed and enforced in accordance with the laws 
of the State of California as applied to contracts made and entirely performed 
therein. The language in all parts of this Agreement shall in all cases be 
construed as a whole according to its fair meaning and not strictly for or 
against either Owner or AtHome.

     13.  Gender; Singular, Plural. When the context of this Agreement 
requires, the neuter gender includes the masculine, the feminine, a partnership 
or corporation or joint venture, and the singular includes the plural.

     14.  Binding Effect. The covenants and agreement contained in this 
Agreement shall be binding on, and inure to the benefit of, the parties hereto 
and on their respective successors and assigns to the extent this Agreement is 
assignable.

     15.  Waiver. The waiver by Owner of any breach of any term, condition or 
covenant, of this Agreement shall not be deemed to be a waiver of such 
provision or any subsequent breach of the same or any other term, condition or 
covenant of this Agreement. No covenant, term or condition of this Agreement 
shall be deemed to have been waived by Owner unless such waiver is in writing 
signed by Owner. This Agreement may be modified only by a written agreement so 
specifying, duly executed by both parties.

     16.  Entire Agreement. This Agreement is the entire agreement between the 
parties, and there are no agreements or representations between the parties 
except as expressed herein. Except as otherwise provided herein, no subsequent 
change or addition to this Agreement shall be binding unless in writing and 
signed by the parties hereto.

     17.  Authority. If AtHome is a corporation or a partnership, each 
individual executing this Agreement on behalf of said corporation or 
partnership, as the case may be, represents and warrants that he is duly 
authorize to execute and deliver this Agreement on behalf of said entity in 
accordance with its corporate bylaws, statement of partnership or certificate 
of limited partnership, as the case may be, and that this Agreement is binding 
upon said entity in accordance with its terms. Owner, at its option, may 
require a copy of such written authorization to enter into this Agreement.

     18.  Attorneys' Fees. If either party brings any action or legal 
proceeding for damages for an alleged breach of any provision of this 
Agreement, or to enforce, protect or establish any term, condition or covenant 
of this Agreement or right of either party, the prevailing party shall be 
entitled to

                                       17
<PAGE>   18
recover as a part of such action or proceedings, or in a separate action 
brought for that purpose, reasonable attorneys' fees and costs, including 
without limitation any and all costs and expenses arising from (a) collection 
efforts, (b) any appellate proceedings, and (c) any bankruptcy, insolvency or 
arbitration proceedings.

      19.   Exhibits. The following exhibits, to which reference is made in 
this Agreement, are deemed incorporated into this Agreement in their entirety 
and made a part hereof:

            Exhibit A   -     Description of North Expansion Parcel

            Exhibit A-1 -     Description of Sears Site

            Exhibit B   -     Description of South Expansion Parcel

            Exhibit C   -     Form of Build to Suit Lease

            Exhibit D   -     General Terms for Build to Suit Lease

            Exhibit E   -     Standard Terms for Purchase of Property

            Exhibit F   -     Basic Site Plans

      20.   Change in Property Description. Owner has recorded on October __, 
1996, in the Official Records of San Mateo County a parcel map creating and 
describing the various parcels comprising the Property (the "Parcel Map"). The 
parties acknowledge and agree the boundaries of the South Expansion Parcel are 
subject to change in Owner's reasonable discretion in relation to the 
development and use of the South Expansion Parcel and certain adjoining 
property, that Owner may from time to time adjust the boundaries of the South 
Expansion Parcel by means of one or more lot line adjustments or similar 
mechanisms, and that the adjusted dimensions of the South Expansion Parcel may 
be as much as one-half (1/2) acre different from the description shown on the 
Parcel Map without affecting the rights and obligations of the parties 
hereunder. No such change in the boundaries of the South Expansion Parcel shall 
detrimentally affect the rights of AtHome under this Agreement. If as a result 
of such adjustment(s) the final dimensions of the South Expansion Parcel are 
more than one-half (1/2) acre different from the description shown on the 
Parcel Map, then AtHome may elect to terminate this Agreement by delivering 
written notice of such election to Owner within ten (10) days after Owner 
notifies AtHome of such discrepancy. If AtHome does not exercise such 
termination right within such 10-day period, then AtHome shall have no further 
right to terminate this Agreement pursuant to this Paragraph 20 and AtHome 
shall have no other rights or remedies with respect to 

                                       18
<PAGE>   19
such change in the final dimensions of the South Expansion Parcel.

        21.   Effect of Subdivision. Owner may from time to time subdivide all
or any portion of the Property into separate legal parcels (each, a "Separate
Parcel"). At any and each time as Owner effectuates any such subdivision of the
Property, this Agreement shall automatically terminate, and Owner and AtHome
shall execute separate agreements for each Separate Parcel (each, a "Replacement
Agreement"). Each Replacement Agreement shall encumber only one of the Separate
Parcels, and shall be in the same form as this Agreement. If AtHome fails or
refuses to execute any such Replacement Agreement upon Owner's request, then
Owner shall have the right to obtain specific performance of AtHome's obligation
to execute such Replacement Agreement. In addition, AtHome hereby irrevocably
constitutes and appoints Owner as its true and lawful attorney in fact, in its
name and in its behalf, to make, execute, acknowledge, deliver, and file any and
all such Replacement Agreements that AtHome so fails or refuses to execute.
AtHome expressly understands and acknowledges that the foregoing special power
of attorney is coupled with an interest, is irrevocable, and shall survive the
dissolution or insolvency of AtHome, or the transfer by AtHome of the whole or
any portion of its interest in this Agreement (provided that any such transfer
shall be subject to the restrictions set forth above in this Agreement).

        22.   No Maintenance Obligations. Owner shall have no obligation
whatsoever to repair or maintain the Property or any buildings at any time
situated on the Property, or any portion thereof.

        23.   Subordination. This Agreement is or may become subject and
subordinate to underlying leases, mortgages, deeds of trust, easements, and
CC&Rs (as defined below) (collectively, "Encumbrances") which may now or
hereafter affect the Property of any portion thereof, and to all renewals,
amendments, modifications, consolidation, replacements and extensions thereof.
Owner shall have the right to cause this Agreement to be and become and remain
subject and subordinate to any and all Encumbrances which are now or may
hereafter be executed covering the Property or any renewals, modifications,
consolidations, replacements or extensions thereof, for the full amount of all
advances made or to be made thereunder and without regard to the time or
character of such advances, together with interest thereon and subject to all
the terms and provisions thereof. In the event of termination of any such lease
or upon the foreclosure of any such mortgage or deed of trust, this Agreement
shall automatically terminate, and the holder or holders of any such Encumbrance
(collectively, "Holder") shall be under no obligation to recognize AtHome's
rights under this Agreement. Within fifteen (15) days after Owner's written
request, AtHome shall execute any and all documents reasonably required by Owner
or the Holder to make this Agreement subordinate to any lien of 


                                       19
<PAGE>   20
the Encumbrance (including, without limitation, subordination to all CC&Rs). 
If AtHome fails to do so, such failure shall constitute a default under this 
Agreement, and it shall be deemed that this Agreement is subordinated to such 
Encumbrance. If Owner elects to purchase the Second Option Subparcel pursuant 
to Paragraph 3, it shall accept title to the Second Option Subparcel as 
provided in Paragraph 3, subject to any and all Encumbrances.

                23.1 CC&Rs. For the purposes of this Agreement, "CC&Rs" shall 
mean any declaration of conditions, covenants and/or restrictions, or similar 
instrument, that now encumbers, or may in the future encumber the Property, as 
adopted by Owner or its successors in interest from time to time, and any 
modifications or amendments thereto.

                23.2 Foreclosure of an Encumbrance. If any Holder acquires 
title to either or both of the North Expansion Parcel or the South Expansion 
Parcel by means of judicial foreclosure, a trustee's sale, or a deed in lieu of 
foreclosure under an Encumbrance (collectively, a "Foreclosure Event"), then 
this Agreement shall automatically terminate as of the date of such Foreclosure 
Event, and Owner shall within a reasonable time after the occurrence of the 
Foreclosure Event refund to AtHome the total remaining amount of the Option 
Deposit then being held by Owner. So long as Owner has given to AtHome prior 
written notice of the impending Foreclosure Event, which notice describes the 
default on which the Foreclosure Event is based (the "Owner's Default"), not 
less than ten (10) days prior to the scheduled occurrence of such Foreclosure 
Event, then if AtHome fails to cure such Owner's Default prior to the 
Foreclosure Event (or, if such Owner's Default is not susceptible of cure by 
AtHome, AtHome fails to pay in full the indebtedness upon which the Foreclosure 
Event is based), effective upon the payment of the above-described refund of 
the Option Deposit to AtHome, Owner shall have no further obligations or 
liability under this Agreement. Owner shall, within five (5) days after 
receipt, give AtHome copies of any and all notices of default received by Owner 
from any Holder with respect to any Encumbrance. If AtHome so cures such 
Owner's Default (or, if such Owner's Default is not susceptible of cure by 
AtHome, AtHome pays in full the indebtedness upon which the Foreclosure Event 
is based) prior to the Foreclosure Event, and the Foreclosure Event does not 
occur, the this Agreement shall remain in full force and effect, and any 
amounts paid by AtHome to such Holder to cure the Owner's Default (the "AtHome 
Advance") shall be credited to AtHome as an offset against the next 
installment(s) of rent due under the Build to Suit Lease for the Option 
Building situated on that portion of the Property with respect to which Owner's 
Default occurred, until such time as AtHome has received a full refund of the 
AtHome Advance, provided that the unpaid balance of the AtHome Advance shall 
bear interest on a per annum basis at the same rate of interest that applied to 
the indebtedness upon which the Foreclosure Event was based. Notwithstanding 
the foregoing, the unpaid balance of any AtHome Advance made with respect to the

                                       20
<PAGE>   21
indebtedness owed by Owner to Ampex Corporation that is secured by the Property 
shall bear interest at the rate of eight percent (8%) per annum. If this 
Agreement expires or is otherwise terminated prior to the execution of a Build 
to Suit Lease for the First Option Building for any reason other than a default 
by AtHome, then Owner shall pay to AtHome an amount equal to the AtHome Advance 
within thirty (30) days after the date the Agreement expires or is otherwise 
terminated. If this Agreement expires or is otherwise terminated prior to the 
execution of a Build to Suit Lease for the First Option Building due to a 
default by AtHome, then AtHome shall not be entitled to receive, and Owner 
shall not be required to pay to AtHome, any refund of the AtHome Advance, or 
any amount in consideration or in lieu thereof, and Owner shall have no further 
obligations or liability under this Agreement; provided, however, that in such 
event AtHome shall be entitled to utilize the unpaid balance of the AtHome 
Advance as an offset against any claim made by Owner against AtHome.

        24.  Estoppel Certificates.  AtHome shall within fifteen (15) days
following written request by Owner execute and deliver to Owner any documents,
including estoppel certificates, in the form prepared by Owner (a) certifying
that this Agreement is unmodified and in full force and effect or, if modified,
stating the nature of such modification and certifying that this Agreement, as
so modified, is in full force and effect, and (b) acknowledging that there are
not, to AtHome's knowledge, any uncured defaults on the part of Owner, or, if
there are uncured defaults on the part of the Owner, stating the nature of such
uncured defaults, (c) evidencing the status of the Agreement as may be required
either by a lender making a loan to owner to be secured by deed of trust or
mortgage covering the Property or a purchaser of the Property from Owner, and
(d) such other matters as may be reasonably requested by Owner. AtHome's failure
to deliver an estoppel certificate within fifteen (15) days after delivery of
Owner's written request therefor shall be conclusive upon AtHome (i) that this
Agreement is in full force and effect, without modification except as may be
represented by Owner, and (ii) that there are now no uncured defaults in Owner's
performance.

        If AtHome fails to so deliver a requested estoppel certificate within 
the prescribed time it shall be conclusively presumed that this Agreement is 
unmodified and in full force and effect except as represented by Owner.

        25.  Transfer of the Property by Owner.  In the event of any conveyance 
of all or any portion of the Property and assignment by Owner of this Agreement 
(including without limitation any transfer of the Property pursuant to a 
Foreclosure Event), Owner shall be and is hereby entirely released from all 
liability under any and all of its covenants and obligations contained in or 
derived from this Agreement occurring after the date of such conveyance and 
assignment with respect to the

                                       21
<PAGE>   22
portion of the Property so transferred by Owner, and AtHome agrees to attorn to 
such transferee provided such transferee assumes Owner's obligations under this 
Agreement; provided, however, that this Paragraph 25 shall be subject to the 
provisions of Paragraph 23.2 above.

     26.  Limitation on Owner's Liability. Owner shall never be personally 
liable under this Agreement, and AtHome shall look solely to Owner's interest 
in the Property for recovery of any damages for breach of this Agreement by 
Owner or on any judgment in connection therewith. None of the persons or 
entities comprising or representing Owner (whether partners, shareholders, 
officers, directors, trustees, employees, beneficiaries, agents or otherwise) 
shall ever be personally liable under this Agreement or for any such damages or 
judgment, and AtHome shall have no right to effect any levy of execution 
against any assets of such persons or entities on account of any such liability 
or judgment. Any lien obtained by AtHome to enforce any such judgment, and any 
levy of execution thereon, shall be subject and subordinate to all Encumbrances 
as specified in Paragraph 23 above. Notwithstanding the foregoing, if under the 
terms of this Agreement Owner is required to return the Option Deposit, or any 
portion thereof, to AtHome, and Owner breaches its obligation to do so in 
accordance with the terms of this Agreement, Owner shall be liable to AtHome 
for the return of the Option Deposit, or such portion thereof.

     27.  Recordation. This Agreement shall not be recorded without the prior 
consent of both Owner and AtHome; provided, however, that upon the written 
request of AtHome, Owner and AtHome shall execute and acknowledge, in 
recordable form, a memorandum of this Agreement in form reasonably acceptable 
to both Owner and AtHome, and shall cause such memorandum to be recorded in the 
Official Records of the County of San Mateo, State of California. Upon 
expiration of the term of this Agreement with respect to any portion of the 
Property, AtHome shall execute, acknowledge and deliver to Owner an appropriate 
instrument prepared by Owner which Owner may then record in the Official 
Records of San Mateo County to expunge this Agreement and any memorandum 
thereof from the public record with respect to such portion of the Property. In 
addition, AtHome hereby irrevocably constitutes and appoints Owner as its true 
and lawful attorney in fact, in its name and in its behalf, to make, execute, 
acknowledge, deliver, and file any and all such instruments that AtHome so 
fails or refuses to execute. AtHome expressly understands and acknowledges that 
the foregoing special power of attorney is coupled with an interest, is 
irrevocable, and shall survive the dissolution or insolvency of AtHome, or the 
transfer by AtHome of the whole or any portion of its interest in this 
Agreement (provided that any such transfer shall be subject to the restrictions 
set forth in this Agreement).

                                       22
<PAGE>   23

        28.     Survival.  This Agreement shall survive the execution of each
Build to Suite Lease.

        IN WITNESS WHEREOF, the parties have executed this Agreement as of the
date first hereinabove set forth.

                                       "Owner"


                                       MARTIN/CAMPUS ASSOCIATES, L.P.,
                                       a Delaware limited partnership

                                       By:  Martin/Redwood Partners
                                            L.P., a California limited
                                            partnership, its General
                                            Partner

                                            By:  The Martin Group of
                                                 Companies, Inc., a
                                                 California corporation,
                                                 its General Partner

                                                 By:  /s/
                                                      --------------------------
                                                 Its:             
                                                      --------------------------


                                       "AtHome"

                                       AT HOME CORPORATION,
                                       A Delaware corporation


                                       By:  /s/ KENNETH A. GOLDMAN
                                            ------------------------------------
                                       Its: CFO
                                            ------------------------------------


                                       By:  
                                            ------------------------------------
                                       Its: 
                                            ------------------------------------





                                       23
<PAGE>   24
  

                FIRST AMENDMENT TO BUILD TO SUIT OPTION AGREEMENT

        THIS FIRST AMENDMENT TO BUILD TO SUIT OPTION AGREEMENT
("Amendment") is made and entered into as of this _____ day of June, 1998, by
and between MARTIN/CAMPUS ASSOCIATES, L.P., a Delaware limited partnership
("Owner"), and AT HOME CORPORATION, a Delaware corporation ("AtHome").

                                 R E C I T A L S

        This Amendment is made and entered into with reference to and upon the
basis of the following facts, intentions and understandings of the parties:

        A. Owner is the owner of (i) that certain real property situated in the
City of Redwood City, County of San Mateo, State of California, which is
depicted on Exhibit A hereto (the "North Expansion Parcel") and (ii) that
certain unimproved real property situated in the City of Redwood City, County of
San Mateo, State of California, which is depicted on Exhibit B hereto (the
"South Expansion Parcel"). The North Expansion Parcel and the South Expansion
Parcel shall be hereinafter from time to time collectively referred to as the
"Property".

        B. Owner and AtHome have entered into that certain Build to Suit Option
Agreement dated as of October 25, 1996 (the "Agreement"), whereby Owner has
granted to AtHome (i) options to lease all or certain portions of the Property
on a build to suit basis and on certain agreed terms and conditions, and (ii) an
option to acquire a portion of the Property, as defined in the Agreement as the
Second Option Subparcel, on certain agreed terms and conditions.

        C. Owner and AtHome now desire to amend the Agreement to cancel the
option to acquire the Second Option Subparcel and to grant in lieu thereof an
option to acquire the South Expansion Parcel and a right to participate in the
proceeds of the sale of the Second Option Subparcel to a third party, upon the
terms and conditions set forth herein.

        D. All capitalized terms not specifically defined in this Amendment
shall have the same meanings ascribed to them in the Agreement.

        NOW, THEREFORE, in consideration of the payment by AtHome to Owner of
the sum of One Hundred Dollars ($100) and for other good and valuable
consideration, the receipt and adequacy of which are hereby acknowledged by
Owner, Owner and AtHome hereby agree as follows:

        1. Second Option. Owner acknowledges that AtHome has timely exercised
the Second Option pursuant to the terms of Paragraph 2.6 of the Agreement.

        2. Third Option. The second sentence of Paragraph 2.7 of the Agreement
is hereby deleted and the following sentence is inserted in place thereof:


                                        1
<PAGE>   25

               "The failure of AtHome so to exercise the Third Option on or
               before the Third Option Notice Date shall terminate AtHome's
               right to exercise the Third Option and shall terminate AtHome's
               right to exercise its option to purchase the South Expansion
               Parcel pursuant to Paragraph 3 unless Tenant delivers the South
               Expansion Parcel Option Notice on or before the Third Option
               Notice Date (in which case AtHome's rights and obligations shall
               be governed by Paragraph 3 below)."

        3. Option to Purchase. Paragraph 3 of the Agreement is deleted in its
entirety and the following Paragraph 3 is inserted in place thereof:

               "3. Option to Purchase.

                      "3.1. Option to Purchase South Expansion Parcel. AtHome
               shall have the option (in lieu of requiring Owner to develop the
               Third Option Building to be situated on the South Expansion
               Parcel) to acquire, on an all cash basis, in the manner set forth
               in Paragraph 3.2, fee title to the South Expansion Parcel. The
               purchase price for the South Expansion Parcel shall be Two
               Million Eighteen Thousand Four Hundred Seventy Seven and 00/100
               Dollars ($2,018,477.00) (the "Base Purchase Price"), subject to
               adjustment as provided herein. The Base Purchase Price has been
               agreed upon by Owner and AtHome based upon the entitlements for
               the South Expansion Parcel obtained as of March 31, 1998 for the
               construction of a building containing 48,569 Rentable Area. Owner
               and AtHome have agreed to adjust the Base Purchase Price in the
               event Owner obtains sufficient entitlements for the construction
               of a building containing up to 110,000 square feet of Rentable
               Area on the South Expansion Parcel. Prior to the Third Option
               Notice Date, Owner shall use reasonable good faith efforts to
               obtain such entitlements. In the event that Owner is successful
               in obtaining entitlements for increased Rentable Area, the Base
               Purchase Price shall be increased by an amount equal to the
               product of Sixty and 00/100 Dollars ($60.00) multiplied by the
               total amount of square feet of Rentable Area approved by the City
               of Redwood City in excess of 48, 569 square feet for the Third
               Option Building to be constructed on the South Expansion Parcel.
               The Base Purchase Price as adjusted is hereinafter referred to as
               the "Adjusted Purchase Price." In order to elect to exercise its
               option to acquire the South Expansion Parcel, AtHome shall
               deliver to Owner, in lieu of its delivery to Owner of AtHome's
               notice exercising the Third Option, a written notice setting
               forth AtHome's exercise of its option to acquire the South
               Expansion Parcel (the "South Expansion Parcel Option Notice").
               The South Expansion Parcel Option Notice shall not be effective
               unless it includes the following: (i) immediately available funds
               in an amount equal to five percent (5%) of the Base Purchase
               Price or the Adjusted Purchase Price, as the case may be, for the
               South Expansion Parcel (the "Deposit"), and (ii) AtHome's
               execution of the liquidated damage provision set forth in Exhibit
               E attached to this Agreement. The Deposit shall be held by the
               Title Company, defined in Exhibit E, in an interest bearing
               account and shall constitute liquidated damages, and shall 


                                       2

<PAGE>   26
               be paid to Owner in the event AtHome fails to consummate the
               purchase of the South Expansion Parcel in accordance with the
               terms of this Paragraph 3, other than as a direct result of
               Owner's failure to perform its obligations under this Paragraph 3
               or Exhibit E. Escrow for the sale of the South Expansion Parcel
               to AtHome shall close thirty (30) days after Owner's receipt of
               the South Expansion Parcel Option Notice, or such other date as
               Owner and AtHome shall mutually agree. AtHome's acquisition of
               the South Expansion Parcel shall be subject to the provisions of
               Paragraph 3.2. If AtHome does not deliver the South Expansion
               Parcel Option Notice to Owner as described above, then AtHome's
               option to purchase the South Expansion Parcel shall terminate and
               cease to be of any force or effect as of the Third Option Notice
               Date. All closing, title insurance and transfer costs, including
               without limitation applicable sales and transfer taxes,
               associated with AtHome's acquisition of the South Expansion
               Parcel shall be paid by Owner and AtHome in accordance with the
               custom in San Mateo County.

                      "3.2. Conditions. The effectiveness of AtHome's option to
               acquire the South Expansion Parcel, as set forth in this
               Paragraph 3, is conditioned on the following: (a) AtHome has not
               previously entered into a Sublet of any Build to Suit Lease or
               the Broadway Lease that requires Owner's consent; and (b) no
               monetary or other material default by AtHome exists under either
               any Build to Suit Lease or the Broadway Lease which remains
               uncured after the giving of any applicable notice and the
               expiration of any applicable cure period. In addition, if any of
               the conditions specified under clauses (a) or (b) above do not
               continue to be satisfied as of the date on which the escrow for
               the sale of the South Expansion Parcel to AtHome is scheduled to
               close, then unless Owner waives in writing any such conditions,
               AtHome's exercise of its right to acquire the South Expansion
               Parcel under this Paragraph 3 shall be null and void, and this
               Agreement shall terminate effective as of the date on which the
               escrow for the sale of the South Expansion Parcel to AtHome was
               scheduled to close.

                      "3.3. Process. Should AtHome exercise its option to
               acquire the South Expansion Parcel within the applicable period
               of time set forth in this Paragraph 3, AtHome's acquisition of
               the South Expansion Parcel shall be carried out on (a) the terms
               and conditions described in this Paragraph 3 (the "Agreed
               Terms"), and (b) the terms and conditions set forth on Exhibit E
               attached to this Agreement (the "Standard Terms"). To the extent
               there is any discrepancy between the Agreed Terms and the
               Standard Terms, the Agreed Terms shall be controlling."

        4. Exhibits. Exhibit E to the Agreement is hereby deleted and Exhibit E
attached hereto is inserted in place thereof. The attached Exhibit E deletes all
references to the defined term "Second Option Subparcel" and inserts in place
thereof the defined term "South Expansion Parcel" and deletes all references to
the "Purchase Price" and inserts in place thereof a reference to either the Base
Purchase Price or the Adjusted Purchase Price, as the case may be. All
references to Exhibit E in the Agreement shall be deemed to reference Exhibit E
attached hereto.


                                       3
<PAGE>   27

        5. Sale of Second Option Subparcel. The following is inserted as a new
Paragraph 29 of the Agreement:

               "29. Sale of Second Option Subparcel. Owner shall use reasonable
               efforts to subdivide the property on which the Second Option
               Building is situated so that one of the buildings comprising the
               Second Option Building becomes situated on one or more legal
               parcels (which parcel or parcels, together with all rights and
               appurtenances thereto, are collectively called the "Second Option
               Subparcel"), separate and apart from any other areas of the
               Project and the North Expansion Parcel. In the event Owner
               succeeds in creating the Second Option Subparcel and and
               subsequently sells the Second Option Subparcel to a third party
               (other than an Affiliate (as defined below) of Owner, At Home
               shall have the right to participate in the Net Sale Proceeds (as
               defined below) provided that close of escrow for such sale occurs
               on or before March 31, 2003, subject to the terms and conditions
               of this Paragraph 29, in consideration for At Home's agreement to
               cancel its option to acquire the Second Option Subparcel. At
               Home's participation shall be equal to seventeen and one/half
               percent (17.5%) of the amount that (i) Net Sales Proceeds exceed
               (ii) the product of Two Hundred Sixty and 00/100 Dollars
               ($260.00) multiplied by the total amount of square foot of the
               Second Option Building located on the Second Option Subparcel at
               the time of the sale. In the event that Owner sells in a single
               transaction the Second Option Subparcel together with all or any
               part of any other areas of or improvements within the Project,
               Owner shall use reasonable good faith efforts to allocate the Net
               Sales Proceeds attributable to the Second Option Subparcel. As
               used herein, Net Sales Proceeds shall mean the Gross Sum paid to
               Owner in connection with the sale, less the sum of the following,
               if and to the extent applicable: all closing costs, escrow fees,
               title insurance costs, recording costs, survey costs, brokerage
               or selling commissions or fees, finder's fees, attorneys' fees,
               closing prorations and other costs or expenses reasonably and
               necessarily incurred, in connection with such sale. As used
               herein, the term "Gross Sum" shall mean the total financial
               consideration paid to Owner in connection with the sale reduced
               by any reserves or purchase price hold-backs required to be
               established by Owner (but only if, and to the extent, such
               reserves or hold-backs actually are retained by the purchaser,
               unless disbursed to Owner for reimbursement of Owner's cost to
               repair or remediate pursuant to the purchase and sale agreement).
               As used herein, the term "Affiliate" shall mean any person or
               entity directly or indirectly controlled by, controlling or under
               common control of Owner or The Martin Group of Companies, Inc., a
               California corporation ("TMG"); any partnership, corporation or
               other entity resulting from the merger or consolidation of Owner;
               any partnership, corporation or other entity in which Owner or a
               constituent partner of Owner or TMG owns an interest; any person
               or entity which acquires all or substantially all of the
               constituent interests in Owner or TMG, any person or entity who
               is a partner or has an ownership interest directly or indirectly
               in any of the foregoing."


                                       4
<PAGE>   28

        6. Credit Against Option Price. The following is inserted as a new
Paragraph 30 of the Agreement:

               "30. Credit Against Option Price. To accommodate Owner's
               construction financing, AtHome has entered into various
               agreements with or for the benefit of Guaranty Federal Bank,
               F.S.B. ("Lender"), including a side letter dated April 6, 1998
               (the "Side Letter"). Under the Side Letter, AtHome may be
               required to cure a default by Owner under Owner's loan agreement
               (which, together with the note, deed of trust and other ancillary
               instruments evidencing and/or securing such loan are called the
               "Construction Loan Documents") with Lender in order to secure the
               release of the South Expansion Parcel from Lender's deed of
               trust. To induce AtHome to enter into the agreements with and for
               the benefit of Lender, Owner hereby covenants and agrees that all
               sums paid by AtHome to Lender, as permitted by the Side Letter or
               otherwise, for the purpose of curing any actual or alleged
               default of Owner under the Construction Loan Documents and/or
               securing a partial release to remove the deed of trust from the
               South Expansion Parcel (together with interest thereon at the
               lesser of the maximum lawful rate or a per annum rate of seven
               percent (7%) above the Federal Reserve discount rate) shall be
               due and payable by Owner upon demand. If Owner fails to make any
               such payment, AtHome shall be entitled to offset the full amount
               of such principal and interest against the Base Purchase Price
               (or the Adjusted Purchase Price, if applicable) for the South
               Expansion Parcel under Paragraph 3.1 above."

        7. Ratification. Except as expressly amended hereby, the Agreement is
hereby ratified and confirmed and shall remain in ful force and effect in all
other respects.

        8. Choice of Law. This Amendment and the rights and obligations of the
parties hereunder shall be construed and enforced in accordance with the laws of
the State of California as applied to contracts made and entirely performed
therein.

               IN WITNESS WHEREOF, the parties have executed this Agreement as
of the date first hereinabove set forth.

                     [SIGNATURES TO FOLLOW ON THE NEXT PAGE]


                                       5
<PAGE>   29

                      "Owner"

                      MARTIN/CAMPUS ASSOCIATES, L.P.,
                      a Delaware limited partnership

                      By:    Martin/Redwood Partners, L.P.,
                             a California limited partnership
                             Its General Partner

                             By:     TMG Redwood LLC,
                                     a California limited liability company
                                     Its General Partner

                                     By:    The Martin Group of Companies, Inc.,
                                            a California corporation
                                            Its Managing Member

                                            By: /s/
                                                --------------------------------
                                            Its: Vice President
                                                --------------------------------


                                            By: 
                                                --------------------------------
                                            Its:
                                                --------------------------------


                      "AtHome"

                      AT HOME CORPORATION,
                      a Delaware corporation

                      By: /s/ KENNETH A. GOLDMAN
                          --------------------------------
                      Its: CFO
                          --------------------------------


                      By: 
                          --------------------------------
                      Its:
                          --------------------------------



                                       6