<PAGE>   1
                                                                    EXHIBIT 4.20


                                SECOND AMENDMENT

         THIS SECOND AMENDMENT (this "Amendment") dated as of July 30, 2001, is
to that certain Credit Agreement dated as of August 31, 2000 (as previously
amended and modified and as amended, modified, supplemented or restated from
time to time, the "Credit Agreement") among PULTE HOMES, INC. f/k/a Pulte
Corporation, a Michigan corporation (the "Borrower"), each of the Material
Subsidiaries of the Borrower (the "Guarantors"; together with the Borrower,
individually a "Credit Party" and collectively the "Credit Parties"), the
Lenders from time to time party thereto (the "Lenders"), BANK OF AMERICA, N.A.,
as Administrative Agent for the Lenders (the "Administrative Agent"), BANK ONE,
NA, as Syndication Agent for the Lenders and COMERICA BANK, as Co-Agent for the
Lenders. Capitalized terms used herein and not otherwise defined shall have the
meanings set forth in the Credit Agreement.

                               W I T N E S S E T H

         WHEREAS, the Borrower has informed the Lenders that it intends to
acquire all of the Capital Stock of Del Webb Corp.;

         WHEREAS, the Borrower and the Lenders have requested certain amendments
to the Credit Agreement in connection with such Acquisition;

         WHEREAS, the amendments requested require the consent of the Required
Lenders; and

         WHEREAS, the Required Lenders have agreed to the amendments on the
terms and conditions set forth herein.

         NOW, THEREFORE, IN CONSIDERATION of the premises and other good and
valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, the parties hereto agree as follows:

                                    SECTION 1
                                    AMENDMENT

         The Credit Agreement is hereby amended as follows:

         1.1 Amendments to Section 1.1.

                  (a) The definition of "Co-Agent" is hereby amended and
         restated in its entirety to read as follows:

                           "Co-Agent" means each of Comerica Bank (or any
                  successor thereto) and SunTrust Bank (or any successor
                  thereto).

                  (b) The definition of "Credit Documents" is hereby amended and
         restated in its entirety to read as follows:


<PAGE>   2

                           "Credit Documents" means this Credit Agreement, the
                  Notes, any Joinder Agreement, the Intercreditor Agreement and
                  all other related agreements and documents issued or delivered
                  hereunder or thereunder or pursuant hereto or thereto.

                  (c) The definition of "Debt to Capitalization Ratio" is hereby
         amended and restated in its entirety to read as follows:

                           "Debt to Capitalization Ratio" means, as of any date,
                  the ratio of (a) Funded Debt less (i) Subordinated Debt issued
                  by the Credit Parties which matures on or after the Maturity
                  Date in an aggregate amount not to exceed $100,000,000 and
                  (ii) all cash and Cash Equivalents held by the Credit Parties
                  in excess of $25,000,000 but less than $100,000,000, to (b)
                  Capitalization.

                  (d) The definition of "Del Webb Acquisition" is hereby added
         to read as follows:

                           "Del Webb Acquisition" means the Acquisition by the
                  Borrower of Del Webb Corp.

                  (e) The definition of "Documentation Agent" is hereby added to
         read as follows:

                           "Documentation Agent" means Citicorp Real Estate,
                  Inc. (or any successor thereto).

                  (f) The definition of "Funded Debt" is hereby amended and
         restated in its entirety to read as follows:

                           "Funded Debt" means, without duplication, the sum of
                  all Indebtedness of the Credit Parties for borrowed money
                  other than Indebtedness owed to a REIT, including, without
                  limitation, (a) all purchase money Indebtedness of the Credit
                  Parties, (b) the principal portion of all obligations of the
                  Credit Parties under Capital Leases, (c) all Guaranty
                  Obligations of the Credit Parties with respect to Indebtedness
                  of another Person, (d) all Indebtedness of another entity
                  secured by a Lien on any property of the Credit Parties
                  whether or not such Indebtedness has been assumed by a Credit
                  Party, and (e) all Indebtedness of any partnership or
                  unincorporated joint venture to the extent a Credit Party is
                  legally obligated or has a reasonable expectation of being
                  liable with respect thereto, net of any assets of such
                  partnership or joint venture.

                  (g) The definition of "Intercreditor Agreement" is hereby
         added to read as follows:

                           "Intercreditor Agreement" means that certain
                  Intercreditor and Subordination Agreement, dated as of the
                  closing date of the Del Webb Acquisition, among the
                  Administrative Agent, on behalf of the Lenders, Citicorp Real
                  Estate, Inc. and Bank One Trust Company, National Association,
                  as secured creditors, Asset Seven Corp., an Arizona
                  corporation, and all other REITs that become a party to the
                  Intercreditor Agreement after the Second Amendment



<PAGE>   3

                  Effective Date, as subordinated creditors, in form and
                  substance satisfactory to the Administrative Agent.

                  (h) The definition of "Permitted Liens" is hereby amended by
         adding the following clause (m) thereto and making the appropriate
         grammatical and punctuation changes:

                           (m) mortgage Liens granted to secure Indebtedness
                  permitted by Section 8.1(j) so long as such mortgage Liens are
                  unrecorded and unperfected.

                  (i) The definition of "Second Amendment Effective Date" is
         hereby added to read as follows:

                           "Second Amendment Effective Date" means July 30,
                  2001.

                  (j) The definition of "REIT" is hereby added to read as
         follows:

                           "REIT" means a collective reference to Asset Seven
                  Corp., an Arizona corporation, and any other Credit Party
                  (other than the Borrower) that properly elects to be taxed as
                  a real estate investment trust under Section 856(c) of the
                  Code and which becomes a party to the Intercreditor Agreement.

         1.2 Amendment to Section 7.2(b). Section 7.2(b) is hereby amended and
restated in its entirety to read as follows:

         7.2 FINANCIAL COVENANTS.

                                  ************

                           (b) Tangible Net Worth. As of the last day of each
                  fiscal quarter of the Borrower (beginning with the fiscal
                  quarter ending September 30, 2000), Tangible Net Worth shall
                  be greater than or equal to (i) prior to the closing of the
                  Del Webb Acquisition, the sum of (A) $800 million, plus (B)
                  50% of the cumulative Net Income (without deduction for
                  losses) earned for each completed fiscal quarter subsequent to
                  March 31, 2000 to the date of determination and (ii) after the
                  closing of the Del Webb Acquisition, the sum of (A) 85% of
                  Tangible Net Worth as of September 30, 2001, plus (B) 50% of
                  the cumulative Net Income (without deduction for losses)
                  earned for each completed fiscal quarter subsequent to
                  September 30, 2001 to the date of determination.

         1.3 Amendment to Section 8.1. Section 8.1 is hereby amended by adding
the following subsection (j) thereto and making the appropriate grammatical and
punctuation changes:

                  8.1 INDEBTEDNESS.

                  No Credit Party will contract, create, incur, assume or permit
         to exist any Indebtedness, except:

                                  ************
<PAGE>   4

                           (j) Indebtedness owing by a Credit Party (other than
                  the Borrower) to a REIT; provided that (i) the Del Webb
                  Acquisition shall have been consummated, (ii) such REIT shall
                  have become a Guarantor pursuant to the terms of Section 7.12,
                  (iii) such REIT shall have entered into the Intercreditor
                  Agreement, (iv) such REIT shall be in compliance with the
                  terms of Section 8.14 and (v) such REIT shall qualify as a
                  real estate investment trust under applicable tax laws.

         1.4 Addition of New Section 8.14. A new Section 8.14 is hereby added to
read as follows:

         SECTION 8.14      RESTRICTIONS ON THE REIT.

                  No REIT will engage in any activities or operations whatsoever
         other than (a) general administrative and other functions permitted by
         law, (b) possessing any promissory notes that evidence the Indebtedness
         permitted by Section 8.1(j) and receiving payments of principal and
         interest on such promissory notes, (c) possessing any other "real
         estate assets" within the meaning of Section 856(c)(5) of the Code for
         purposes of satisfying the requirements for a real estate investment
         trust under applicable tax laws, (d) making or consenting to dividends
         and distributions to a Credit Party and (e) any other functions or
         other activities that are now or may become required or permitted of a
         REIT for purposes of satisfying the requirements for a real estate
         investment trust under applicable tax laws. Notwithstanding the terms
         of Sections 7.12, 8.1 and 8.2, (i) each REIT will at all times be a
         Guarantor and will not be released from its Guaranty Obligations under
         this Credit Agreement if it shall cease to be a Material Subsidiary,
         (ii) no REIT will incur any Indebtedness other than (A) its Guaranty
         Obligations under this Credit Agreement and (B) accounts payable
         incurred for general administrative and other functions of such REIT
         permitted by law in an amount not to exceed $100,000 at any time
         outstanding and (iii) no REIT will contract, create, incur, assume or
         permit to exist any Lien with respect to any of its property or assets
         of any kind (whether real or personal, tangible or intangible), whether
         now owned or after acquired, except for Liens in favor of the
         Administrative Agent and Permitted Liens relating to the possession and
         operation of its real property and other assets.

         1.5 Addition of New Section 10.10. A new Section 10.10 is hereby added
to read as follows:

                  SECTION 10.10 AUTHORIZATION OF INTERCREDITOR AGREEMENT.

                  Each of the Lenders hereby authorizes the Administrative Agent
         to enter into the Intercreditor Agreement on their behalf and to carry
         out the responsibilities and exercise the powers afforded the
         Administrative Agent therein.

         1.6 Addition of Agents. The following agents are hereby added to the
cover page and preamble of the Credit Agreement:

                           Citicorp Real Estate, Inc., as Documentation Agent
                           SunTrust Bank, as Co-Agent



<PAGE>   5

         1.7 Amendment to Schedule 1.1(a). Schedule 1.1(a) to the Credit
Agreement is hereby updated and replaced with the Schedule 1.1(a) attached
hereto.


                                   SECTION 2
                                 MISCELLANEOUS

         2.1 Ratification. The term "Credit Agreement" as used in each of the
Credit Documents shall hereafter mean the Credit Agreement as amended by this
Amendment. Except as herein specifically agreed, the Credit Agreement is hereby
ratified and confirmed and shall remain in full force and effect according to
its terms.

         2.2 Representations. Each of the Credit Parties and the Lenders party
hereto represents and warrants as follows:

                  (a) It has taken all necessary action to authorize the
         execution, delivery and performance of this Amendment.

                  (b) This Amendment has been duly executed and delivered by
         such Person and constitutes such Person's legal, valid and binding
         obligations, enforceable in accordance with its terms, except as such
         enforceability may be subject to (i) bankruptcy, insolvency,
         reorganization, fraudulent conveyance or transfer, moratorium or
         similar laws affecting creditors' rights generally and (ii) general
         principles of equity (regardless of whether such enforceability is
         considered in a proceeding at law or in equity).

                  (c) No consent, approval, authorization or order of, or
         filing, registration or qualification with, any court or Governmental
         Authority or third party is required in connection with the execution,
         delivery or performance by such Person of this Amendment.

         2.3 No Conflicts. Neither the execution and delivery of this Amendment,
nor the consummation of the transactions contemplated herein, nor performance of
and compliance with the terms and provisions hereof by each Credit Party will
(a) violate, contravene or conflict with any provision of its articles or
certificate of incorporation, bylaws or other organizational or governing
document, (b) violate, contravene or conflict with any law, rule, regulation,
order, writ, judgment, injunction, decree or permit applicable to it, (c)
violate, contravene or conflict with contractual provisions of, or cause an
event of default under, any material indenture, loan agreement, mortgage, deed
of trust, contract or other agreement or instrument to which it is a party or by
which it may be bound or (d) result in or require the creation of any Lien upon
or with respect to its properties.

         2.4 No Default. The Credit Parties represent and warrant to the Lenders
that (a) the representations and warranties of the Credit Parties set forth in
Section 6 of the Credit Agreement are true and correct as of the date hereof and
(b) no event has occurred and is continuing which constitutes a Default or an
Event of Default.

         2.5 General Release. In consideration of the Required Lenders entering
into this Amendment, the Credit Parties hereby release the Administrative Agent,
the Lenders and their respective officers, employees, representatives, agents,
counsel and directors from any and all actions, causes of action, claims,
demands, damages and liabilities of whatever kind or nature, in



<PAGE>   6

law or in equity, now known or unknown, suspected or unsuspected to the extent
that any of the foregoing arises from any action or failure to act under any
Credit Document on or prior to the date hereof.

         2.6 Credit Document. This Amendment shall constitute a Credit Document
under the terms of the Credit Agreement.

         2.7 Condition Precedent. This Amendment shall be effective upon receipt
by the Administrative Agent of a counterpart signature (via facsimile or
otherwise) to this Amendment from each of the Credit Parties and the Required
Lenders.

         2.8 Counterparts; Telecopy. This Amendment may be executed in any
number of counterparts, each of which when so executed and delivered shall be an
original, but all of which shall constitute one and the same instrument.
Delivery of an executed counterpart by telecopy shall be effective as an
original and shall constitute a representation that an original will be
delivered.

         2.9 Expenses of Administrative Agent. The Credit Parties agree to pay
all reasonable costs and expenses of the Administrative Agent in connection with
the preparation, execution and delivery of this Amendment, including without
limitation the reasonable fees and expenses of Moore & Van Allen PLLC, special
counsel to the Administrative Agent.

         2.10 GOVERNING LAW. THIS AMENDMENT AND THE RIGHTS AND OBLIGATIONS OF
THE PARTIES HEREUNDER SHALL BE GOVERNED BY AND CONSTRUED AND INTERPRETED IN
ACCORDANCE WITH THE LAWS OF THE STATE OF NORTH CAROLINA.

                  [Remainder of Page Intentionally Left Blank]


         IN WITNESS WHEREOF, each of the parties hereto has caused a counterpart
of this Amendment to be duly executed and delivered as of the date and year
first above written.

BORROWER:
                            PULTE HOMES, INC. F/K/A PULTE CORPORATION,
                            a Michigan corporation

                            By:
                               --------------------------------------------

                            Name:
                                 ------------------------------------------

                            Title:
                                  -----------------------------------------




<PAGE>   7


GUARANTORS:

                               ABACOA HOMES, INC.,
                               a Florida corporation

                               DIVOSTA AND COMPANY, INC.,
                               a Florida corporation

                               DIVOSTA BUILDING CORPORATION,
                               a Florida corporation

                               DIVOSTA HOMES, INC.,
                               a Florida corporation

                               FLORIDA BUILDING PRODUCTS, INC.,
                               a Florida corporation

                               FLORIDA CLUB HOMES, INC.,
                               a Florida corporation

                               HAMMOCK RESERVE DEVELOPMENT
                               COMPANY, a Florida corporation

                               HOMESITE SOLUTIONS CORPORATION,
                               a Michigan corporation

                               ISLAND WALK DEVELOPMENT COMPANY,
                               a Florida corporation

                               PB VENTURE L.L.C.,
                               a Michigan limited liability company

                               PN II, INC.,
                               a Nevada corporation

                               PULTE DEVELOPMENT CORPORATION,
                               a Michigan corporation

                               PULTE DIVERSIFIED COMPANIES, INC.,
                               a Michigan corporation

                               PULTE FINANCIAL COMPANIES, INC.,
                               a Michigan corporation

                               PULTE HOME CORPORATION,
                               a Michigan corporation


<PAGE>   8


                               PULTE HOME CORPORATION OF NEW
                               ENGLAND, a Michigan corporation

                               PULTE HOME CORPORATION OF THE
                               DELAWARE VALLEY, a Michigan corporation

                               PULTE HOMES OF GREATER KANSAS
                               CITY, INC., a Michigan corporation

                               PULTE HOMES OF MICHIGAN
                               CORPORATION, a Michigan corporation

                               PULTE HOMES OF MINNESOTA
                               CORPORATION, a Minnesota corporation

                               PULTE HOMES OF OHIO CORPORATION,
                               an Ohio corporation

                               PULTE HOMES OF SOUTH CAROLINA, INC.,
                               a Michigan corporation

                               PULTE HOMES OF TEXAS, L.P.,
                               a Texas limited partnership

                                        By:  PN I, INC., a Nevada corporation,
                                             its general partner

                               PULTE LAND DEVELOPMENT
                               CORPORATION, a Michigan corporation

                               PULTE LIFESTYLE COMMUNITIES, INC.,
                               a Michigan corporation

                               PULTE - IN CORPORATION,
                               a Michigan corporation

                               RADNOR HOMES, INC.,
                               a Michigan corporation

                               RIVERWALK OF THE PALM BEACHES
                               DEVELOPMENT COMPANY, INC.,
                               a Florida corporation

                               RN ACQUISITION 2 CORP.,
                               a Nevada corporation


<PAGE>   9



                               SEAN/CHRISTOPHER HOMES, INC.,
                               a Michigan corporation

                               VILLAGE WALK DEVELOPMENT
                               COMPANY, INC., a Florida corporation

                               WIL CORPORATION,
                               a Michigan corporation


                               By:
                                  ----------------------------------------------
                               Name:
                                    --------------------------------------------
                               Title:
                                     -------------------------------------------


<PAGE>   10



LENDERS:

                           BANK OF AMERICA, N.A.,
                           individually in its capacity as a Lender and
                           in its capacity as the Administrative Agent

                           By:
                              --------------------------------------------------
                           Name:
                                ------------------------------------------------
                           Title:
                                 -----------------------------------------------


<PAGE>   11


                           BANK ONE, NA,
                           individually in its capacity as a Lender and
                           in its capacity as the Syndication Agent

                           By:
                              --------------------------------------------------
                           Name:
                                ------------------------------------------------
                           Title:
                                 -----------------------------------------------



<PAGE>   12


                           COMERICA BANK,
                           individually in its capacity as a Lender and
                           in its capacity as a Co-Agent

                           By:
                              --------------------------------------------------
                           Name:
                                ------------------------------------------------
                           Title:
                                 -----------------------------------------------


<PAGE>   13


                           SUNTRUST BANK


                           By:
                              --------------------------------------------------
                           Name:
                                ------------------------------------------------
                           Title:
                                 -----------------------------------------------


<PAGE>   14


                           MICHIGAN NATIONAL BANK


                           By:
                              --------------------------------------------------
                           Name:
                                ------------------------------------------------
                           Title:
                                 -----------------------------------------------


<PAGE>   15


                           PNC BANK, NATIONAL ASSOCIATION


                           By:
                              --------------------------------------------------
                           Name:
                                ------------------------------------------------
                           Title:
                                 -----------------------------------------------


<PAGE>   16


                           THE FUJI BANK, LIMITED


                           By:
                              --------------------------------------------------
                           Name:
                                ------------------------------------------------
                           Title:
                                 -----------------------------------------------




<PAGE>   17


                           CREDIT LYONNAIS NEW YORK BRANCH


                           By:
                              --------------------------------------------------
                           Name:
                                ------------------------------------------------
                           Title:
                                 -----------------------------------------------


<PAGE>   18


                           THE NORTHERN TRUST COMPANY


                           By:
                              --------------------------------------------------
                           Name:
                                ------------------------------------------------
                           Title:
                                 -----------------------------------------------



<PAGE>   19


                           COMPASS BANK


                           By:
                              --------------------------------------------------
                           Name:
                                ------------------------------------------------
                           Title:
                                 -----------------------------------------------


<PAGE>   20


                           CITICORP REAL ESTATE, INC.


                           By:
                              --------------------------------------------------
                           Name:
                                ------------------------------------------------
                           Title:
                                 -----------------------------------------------


<PAGE>   21


                           CREDIT SUISSE FIRST BOSTON


                           By:
                              --------------------------------------------------
                           Name:
                                ------------------------------------------------
                           Title:
                                 -----------------------------------------------



<PAGE>   22




                                 Schedule 1.1(a)

                      Revolving Loan Commitment Percentages
<TABLE>
<CAPTION>
-------------------------------------------------------------------------------------------------------------------------------
                     LENDER                                  REVOLVING LOAN                         REVOLVING LOAN
                                                               COMMITMENT                       COMMITMENT PERCENTAGE
-------------------------------------------------------------------------------------------------------------------------------
<S>                                                         <C>                                 <C>
Bank of America, N.A.                                         $100,000,000                           17.857142857%
-------------------------------------------------------------------------------------------------------------------------------
Bank One, NA                                                  $100,000,000                           17.857142857%
-------------------------------------------------------------------------------------------------------------------------------
Citicorp Real Estate, Inc.                                     $85,000,000                           15.178571429%
-------------------------------------------------------------------------------------------------------------------------------
Comerica Bank                                                  $50,000,000                           8.928571429%
-------------------------------------------------------------------------------------------------------------------------------
SunTrust Bank                                                  $50,000,000                           8.928571429%
-------------------------------------------------------------------------------------------------------------------------------
Credit Lyonnais New York Branch                                $40,000,000                           7.142857143%
-------------------------------------------------------------------------------------------------------------------------------
Michigan National Bank                                         $35,000,000                           6.250000000%
-------------------------------------------------------------------------------------------------------------------------------
PNC Bank, National Association                                 $35,000,000                           6.250000000%
-------------------------------------------------------------------------------------------------------------------------------
The Fuji Bank, Limited                                         $20,000,000                           3.571428571%
-------------------------------------------------------------------------------------------------------------------------------
Compass Bank                                                   $20,000,000                           3.571428571%
-------------------------------------------------------------------------------------------------------------------------------
The Northern Trust Company                                     $15,000,000                           2.678571429%
-------------------------------------------------------------------------------------------------------------------------------
Credit Suisse First Boston                                     $10,000,000                           1.785714286%
-------------------------------------------------------------------------------------------------------------------------------

-------------------------------------------------------------------------------------------------------------------------------
TOTAL:                                                        $560,000,000                               100%
-------------------------------------------------------------------------------------------------------------------------------
</TABLE>