<PAGE>   1

                                                                   Exhibit 10.16

                               THIRD AMENDMENT TO
                    WAREHOUSING CREDIT AND SECURITY AGREEMENT

         This Third Amendment to Warehousing Credit and Security Agreement (this
"Amendment"), is entered into as of the 15th day of December 1998, by and
between CONSTRUCTION PORTFOLIO FUNDING, INC., a Texas corporation (the
"Company"), and BANK UNITED, a federal savings bank ("Lender"). Capitalized
terms used but not defined herein have the meanings assigned to them in that
certain Warehousing Credit and Security Agreement (the "Credit Agreement") dated
effective as of December 30, 1997, by and between the Company and Lender, as the
same has been or may be amended or supplemented from time to time.

         Section 1. Recitals. The Company and Lender desire to amend the Credit
Agreement, subject to the terms and conditions of this Amendment. Therefore, The
Company and Lender hereby agree as follows, intending to be legally bound:

         Section 2. Amendments. The Credit Agreement is hereby amended and
supplemented as follows:

         (a) Section 1.1 of the Credit Agreement is hereby amended by the
         amendment or addition of the following definitions:

                           All references to the "Construction Policies and
                  Procedures Manual" shall hereafter be references to "Credit
                  and Underwriting Policies for Real Estate Lending," a copy of
                  which is attached hereto as Exhibit B.

                           "Aged Loans" means, collectively, (a) any Residential
                  Construction Loan for any Sold Home and Speculative Home
                  included in Collateral for a period of more than three hundred
                  sixty (360) days, (b) any Residential Construction Loan for
                  Model Homes included in Collateral for a period of more than
                  six hundred thirty (630) days, (c) any Residential A&D Loan
                  included in Collateral for a period of more than six hundred
                  thirty (630) days, and (d) any Commercial Mortgage Loan
                  included in the Collateral for a period of more than three
                  hundred sixty-five (365) days.

                           "Appraisal" means (a) with respect to each Home to be
                  constructed under any Residential Construction Loan, a current
                  fair market value appraisal, accepted by the Company in
                  accordance with the Construction Loan Agreement, that
                  appraises on a "completed value" basis the Home to be
                  constructed on a specified Lot; (b) with respect to any Lot
                  under any Residential Construction Loan or any Residential
                  Land under any residential A&D Loan, a current fair market
                  value appraisal of such Lot or Residential Land; (c) with
                  respect to any Consumer Lot Loan, a current fair market
                  appraisal of the lot to be acquired with proceeds of such
                  Consumer Lot Loan; (d) with respect to any Consumer
                  Construction Loan, a current fair market value appraisal that
                  appraises on a "completed value" basis the Home to be
                  constructed from the proceeds of such Consumer Construction
                  Loan and the lot on which such Home is located; and (e) with
                  respect to any Commercial Mortgage Loan, a current fair market
                  value appraisal of the real property (including all
                  improvements thereon) 

<PAGE>   2

                  securing such Commercial Mortgage Loan; each of the foregoing
                  appraisals must satisfy the appraisal requirements of the
                  Office of Thrift Supervision ("OTS") pertaining to that
                  particular loan, as amended from time to time, provided,
                  however, that the Company shall not have any obligation to
                  conform to any changes in the OTS appraisal requirements
                  occurring after the effective date herewith unless Lender has
                  notified the Company in writing of such changes.

                           "Appraisal Value" means (a) with respect to each Lot
                  and Home to be constructed thereon under any Residential
                  Construction Loan, the fair market value of such Lot and Home,
                  upon one hundred percent (100%) completion of all construction
                  thereof in accordance with the Plans and Specifications for
                  such Home plus lot value for such Lot, all as determined by
                  the Appraisal; (b) with respect to a Lot on which a Home is to
                  be constructed thereon under any Residential Construction
                  Loan, the fair market value attributable to such Lot in the
                  Appraisal; (c) with respect to Residential Land under any
                  Residential A&D Loan, the fair market value attributable to
                  such Residential Land in the Appraisal; (d) with respect to
                  each Lot and Home to be constructed thereon under any Consumer
                  Construction Loan, the fair market value of such Lot and Home,
                  upon one hundred percent (100%) completion of all construction
                  of such Home plus lot value for such Lot, all as determined by
                  the Appraisal; (e) with respect to a Lot on which a Home is to
                  be constructed thereon under any Consumer Lot Loan, the fair
                  market value attributable to such Lot in the Appraisal; and
                  (f) with respect to the property securing a Commercial
                  Mortgage Loan, the fair market value of such property and all
                  improvements thereon, all as determined by the Appraisal.

                           "Assignment Documents" means originals of such
                  instruments, documents, agreements, assignments, certificates,
                  UCC Financing Statements, allonges or endorsements, in form
                  and substance satisfactory to Lender in Lender's sole
                  discretion, which Lender reasonably determines are necessary
                  or appropriate to evidence and/or effectuate the assignment to
                  Lender of all of the Company's right, title and interest in
                  and to any and all Residential Construction Loans, Residential
                  A&D Loans, Consumer Construction Loans, Consumer Lot Loans,
                  and Commercial Mortgage Loans in respect of which Advances
                  have been made by the Lender hereunder, including, without
                  limitation, all Consumer Loan Documents evidencing Consumer
                  Construction Loans and Consumer Lot Loans, all Construction
                  Loan Documents evidencing such Residential Construction Loans
                  and Residential A&D Loans, and all Commercial Loan Documents
                  evidencing Commercial Mortgage Loans, and the proceeds thereof
                  and Lender's perfection of a valid first priority lien thereon
                  or therein, including, without limitation, the UCC Financing
                  Statement.

                           "Commercial Loan Documents" shall mean, with respect
                  to any Commercial Mortgage Loan, any and all agreements or
                  instruments now or hereafter executed and delivered by any
                  Person in connection with, or as security for the payment or


--------------------------------------------------------------------------------

                                                                          Page 2
<PAGE>   3

                  performance of such Commercial Mortgage Loan, as such
                  Commercial Loan Documents may be supplemented, modified, or
                  amended.

                           "Commercial Loan Guidelines" means guidelines for
                  commercial loans set forth in the "Credit and Underwriting
                  Policies for Real Estate Lending," a copy of which is attached
                  hereto as Exhibit B.

                           "Commercial Mortgage Loan" shall mean any Mortgage
                  Loan that (a) is evidenced by a Mortgage Note secured by a
                  First Mortgage covering improved commercial real property, (b)
                  has closed not more than ninety (90) days prior to the date of
                  any determination, (c) is not in default in the payment of
                  principal and interest or in the performance of any obligation
                  under the note or mortgage evidencing or securing such loan
                  for a period greater than thirty (30) days, (d) is not in
                  foreclosure or subject to any claim for any credit, allowance,
                  or adjustment, and (e) complies with the Commercial Loan
                  Guidelines and the requirements of the Credit and Underwriting
                  Policies in all material respects.

                           "Commercial Note" means a promissory note executed by
                  any Person to the Company (or otherwise payable to the
                  Company) to evidence a Commercial Mortgage Loan, as such note
                  may be from time to time renewed, extended, rearranged,
                  modified, amended, restated, or replaced.

                           "Eligible Commercial Loan" means a Commercial
                  Mortgage Loan that, at all times during the term of this
                  Agreement, (a) is evidenced by Commercial Loan Documents that
                  are substantially in the forms previously approved, in
                  writing, by the Lender in its reasonable discretion; (b) is
                  validly pledged to the Lender, subject to no other Liens; (c)
                  is not in default in the payment of principal and interest for
                  a period of more than thirty (30) days; (d) is not in default
                  in the performance of any obligation under the Commercial Loan
                  Documents evidencing or securing such Eligible Commercial
                  Loan, that has not been cured by the borrower; (e) is not
                  subject to a bankruptcy or an act of fraud by the borrower
                  under such Eligible Commercial Loan, as the case may be; (f)
                  complies with all applicable Commercial Loan Guidelines in all
                  material respects, (g) is for a loan amount that does not
                  exceed its Loan Value; and (h) may not comply with all of the
                  foregoing terms but is otherwise on terms acceptable to the
                  Lender in its sole discretion as indicated by Lender's
                  specific written or oral waiver of non-compliance with such
                  foregoing terms.

                           "The definition of "Loan Value" is supplemented by
                  the addition of the following subsection (f):

                           "(f) with respect to each Commercial Mortgage Loan,
                           the least of (i) the Appraisal Value of the real
                           property (including all improvements thereon)
                           securing such Commercial Mortgage Loan; (ii) the
                           original principal amount of the Commercial Note
                           evidencing such Commercial Mortgage Loan; or (iii)


--------------------------------------------------------------------------------

                                                                          Page 3

<PAGE>   4

                           the outstanding principal balance of the Commercial
                           Note evidencing such Commercial Mortgage Loan."

                           "Pledged Mortgage" means any Residential Construction
                  Loan, Residential A&D Loan, Aged Loan, Consumer Construction
                  Loan, Consumer Lot Loan or Commercial Mortgage Loan, included
                  in the Collateral.

                           "Request for Advance" means, for Mortgage Loans that
                  are not Commercial Mortgage Loans, a disbursement request
                  summary accompanied by a Warehouse Loan Balance Summary,
                  substantially in the form of Exhibits "L", "M" and "R",
                  respectively, attached hereto, specifying the amount of the
                  requested Advance, the Residential Construction Loans,
                  Residential A&D Loans, Consumer Construction Loans, Consumer
                  Lot Loans, and Commercial Mortgage Loans, and (if not a
                  Commercial Mortgage Loan) the construction costs specified in
                  the applicable Construction Costs Schedule relating to such
                  loans that will be funded with the proceeds of such Advance
                  and a request that Lender make such Advance in accordance with
                  the terms of this Agreement. Notwithstanding the foregoing, if
                  the Advance is to be made against a Commercial Mortgage Loan,
                  "Request for Advance" shall mean the Form attached hereto as
                  Exhibit R, accompanied by documentation set forth in Exhibit
                  A-1 attached hereto.

                           "Termination Date" shall mean June 14, 1999, or such
                  earlier date upon which Lender's obligation to fund shall be
                  terminated pursuant to the terms of this Agreement.

                           "Year 2000 Issue" shall mean the failure of computer
                  software, hardware, and firmware systems and equipment
                  containing embedded computer chips to properly receive,
                  transmit, process, manipulate, store, retrieve, re-transmit,
                  or in any other way utilize data and information due to the
                  occurrence of the year 2000 or the inclusion of dates before,
                  on, or after January 1, 2000 (including, without limitation,
                  September 9, 1999, and February 29, 2000.

         (b) Section 2.1 of the Credit Agreement is deleted in its entirety, and
         the following is substituted therefor:

                  "2.1. The Commitment.

                  "(a) Subject to the terms and conditions of this Agreement and
                  provided no Default or Event of Default has occurred and is
                  continuing, the Lender agrees, from time to time during the
                  period from the date hereof to and including the Termination
                  Date, to make Advances to the Company, provided the total
                  aggregate principal amount outstanding at any one time of all
                  such Advances shall not exceed FORTY MILLION DOLLARS
                  ($40,000,000.00) at any time after the date hereof. The
                  obligation of the Lender to make Advances hereunder up to such
                  limit is 


--------------------------------------------------------------------------------

                                                                          Page 4
<PAGE>   5

                  hereinafter referred to as the "Commitment." Within the
                  Commitment, the Company may borrow, repay, and reborrow. All
                  Advances under this Agreement shall constitute a single
                  indebtedness, and all of the Collateral shall be security for
                  the Note and for the performance of all the Obligations of the
                  Company to the Lender.

                  "(b) Advances shall be used by the Company solely for the
                  purpose of funding or purchasing and/or funding Residential
                  Construction Loans, Residential A&D Loans, Consumer
                  Construction Loans, Consumer Lot Loans, and Commercial
                  Mortgage Loans, as specified in the Request for Advance, and
                  none other, and shall be made at the request of the Company in
                  the manner hereinafter provided in Section 2.2, against the
                  pledge of such Residential Construction Loans, Residential A&D
                  Loans, Consumer Construction Loans, Consumer Lot Loans, and
                  Commercial Mortgage Loans, as the case may be, and such other
                  collateral as is set forth in section 3.1 hereof as Collateral
                  therefor. Advances shall also be subject to the following
                  restrictions:

                           "(1) No Advance shall be made against a Residential
                           Construction Loan, a Residential A&D Loan, an Aged
                           Loan, a Consumer Construction Loan, or a Consumer Lot
                           Loan that is not an Eligible Construction Loan.

                           "(2) No Advance shall be made against a Commercial
                           Mortgage Loan that is not an Eligible Commercial
                           Loan.

                           "(3) The aggregate amount of all Advances against
                           Residential Construction Loans outstanding at any one
                           time shall not exceed FORTY MILLION AND NO/100
                           DOLLARS ($40,000,000/00). The aggregate face amount
                           of all Residential Construction Loans in respect of
                           which an Advance has been made by the Lender
                           hereunder shall not exceed in the aggregate Eighty
                           Million and No/100 Dollars ($80,000,000.00).

                           "(4) The aggregate amount of all Advances against
                           Model Homes under all Residential Construction Loans
                           outstanding at any one time shall not exceed Six
                           Million and No/100 Dollars ($6,000,000.00). The
                           aggregate face amount of all Residential Construction
                           Loans for Model Homes in respect of which an Advance
                           has been made by the Lender hereunder shall not
                           exceed in the aggregate Twelve Million and No/100
                           Dollars ($12,000,000.00).

                           "(5) The aggregate amount of all Advances against
                           Speculative Homes under all Residential Construction
                           Loans outstanding at any one time shall not exceed
                           Sixteen Million and No/100 Dollars ($16,000 000.00).
                           The aggregate face amount of all Residential
                           Construction Loans for Speculative Homes in respect
                           of which an Advance has been made by the Lender
                           hereunder shall not exceed in the aggregate
                           Thirty-two Million and No/100 Dollars
                           ($32,000,000.00).


--------------------------------------------------------------------------------

                                                                          Page 5
<PAGE>   6

                           "(6) The aggregate amount of all Advances against
                           Residential A&D Loans and Commercial Mortgage Loans
                           outstanding at any one time shall not exceed Eight
                           Million and No/100 Dollars ($8,000,000.00); provided,
                           however, that in no event shall the aggregate amount
                           of Advances outstanding against Commercial Mortgage
                           Loans exceed Four Million Dollars ($4,000,000). The
                           aggregate face amount of all Residential A&D Loans
                           and Commercial Mortgage Loans in respect of which an
                           Advance has been made by the Lender hereunder shall
                           not exceed in the aggregate Sixteen Million and
                           No/100 Dollars ($16,000,000.00); provided, however,
                           that in no event shall the aggregate face amount of
                           all Commercial Mortgage Loans in respect of which an
                           Advance has been made by lender exceed in the
                           aggregate Eight Million Dollars ($8,000,000).

                           "(7) The aggregate amount of all Advances against
                           Residential A&D Loans, Model Homes, and Speculative
                           Homes outstanding at any one time shall not exceed
                           Twenty Million and No/100 Dollars ($20,000,000.00).
                           The aggregate face amount of all Residential A&D
                           Loans in respect of which an Advance has been made by
                           the Lender hereunder shall not exceed in the
                           aggregate Forty Million and No/100 Dollars
                           ($40,000,000.00).

                           "(8) The aggregate amount of all Advances against
                           Aged Loans (that are not Commercial Mortgage Loans)
                           outstanding at any one time shall not exceed Six
                           Million and No/100 Dollars ($6,000,000.00). The
                           aggregate face amount of all Aged Loans (that are not
                           Commercial Mortgage Loans) in respect of which an
                           Advance has been made by the Lender hereunder shall
                           not exceed in the aggregate Twelve Million and No/100
                           Dollars ($12,000,000.00).

                           "(9) The aggregate amount of all Advances against
                           Aged Loans (that are Commercial Mortgage Loans)
                           outstanding at any one time shall not exceed One
                           Million and No/100 Dollars ($1,000,000.00). The
                           aggregate face amount of all Aged Loans (that are
                           Commercial Mortgage Loans) in respect of which an
                           Advance has been made by the Lender hereunder shall
                           not exceed in the aggregate Two Million and No/100
                           Dollars ($2,000,000.00).

                           "(10) The aggregate amount of all Advances against
                           Consumer Construction Loans and Consumer Lot Loans
                           outstanding at any one time shall not exceed Four
                           Million and No/100 Dollars ($4,000,000.00). The
                           aggregate face amount of all Consumer Construction
                           Loans and Consumer Lot Loans in respect of which an
                           Advance has been made by the Lender hereunder shall
                           not exceed in the aggregate Eight Million and No/100
                           Dollars ($8,000,000.00).


--------------------------------------------------------------------------------

                                                                          Page 6
<PAGE>   7

                  "(c) No Advance shall exceed the following amounts applicable
                  to the type of Collateral acquired with proceeds of the
                  Advance, determined as of the date the Collateral is pledged
                  to Lender:

                           "(1) with respect to Residential Construction Loans,
                           no Advance shall exceed an amount equal to ninety
                           percent (90%) of the amount of the Construction Loan
                           Advance under such residential Construction Loan to
                           be funded from the proceeds of the Advance.

                           "(2) with respect to any Residential A&D Loans that
                           has a loan-to-value ratio equal to or less than 70%
                           and a loan-to-cost ratio equal to or less than 90%,
                           no Advance shall exceed an amount equal to ninety
                           percent (90%) of the amount of the Construction Loan
                           Advance under such Residential A&D Loan to be funded
                           from the proceeds of the Advance.

                           "(3) with respect to Residential A&D Loans that
                           exceed the ratios set forth in Section 2.1(c)(2)
                           above, no Advance shall exceed an amount equal to
                           eighty percent (80%) of the amount of the
                           Construction Loan Advance under such Residential A&D
                           Loan to be funded from the proceeds of the Advance.

                           "(4) with respect to Commercial Mortgage Loans, no
                           Advance shall exceed an amount equal to 75% of the
                           Loan Value of such Commercial Mortgage Loan.

                           "(5) with respect to Aged Loans that are not
                           Commercial Mortgage Loans, no Advance shall exceed an
                           amount equal to sixty-five percent (65%) of the
                           principal amount outstanding of such Aged Loan prior
                           to any principal reductions required and received by
                           the Company from its borrower.

                           "(6) with respect to Aged Mortgage Loans that are
                           Commercial Mortgage Loans, no Advance shall exceed an
                           amount equal to sixty-five percent (65%) of the Loan
                           Value of such Commercial Mortgage Loan, prior to any
                           principal reductions required and received by the
                           Company from its borrower.

                           "(7) with respect to Consumer Lot Loans, no Advance
                           shall exceed an amount equal to eighty percent (80%)
                           of the amount of the Advance made by the Company
                           under such Consumer Lot Loan to be funded from the
                           proceeds of the Advance.

                           "(8) with respect to Consumer Construction Loans, no
                           Advance shall exceed an amount equal to ninety
                           percent (90%) of the amount of the Advance made by
                           the Company under such Consumer Construction Loan to
                           be funded from the proceeds of the Advance.


--------------------------------------------------------------------------------

                                                                          Page 7
<PAGE>   8

                           "(9) with respect to Aged Loans that are Acquired
                           Loans and that have been included in Collateral for
                           more than 450 days but less than 720 days, no Advance
                           shall exceed an amount equal to 50% of the principal
                           amount outstanding of such Aged Loan as of December
                           30, 1997.

         (c) Section 2.4(a)(3) is amended to read as follows:

                  "(3) The unpaid amount of each advance outstanding against an
                  Aged Loan (that is not a Commercial Mortgage Loan) shall bear
                  interest from the later to occur of the date such Aged Loan
                  became an Aged Loan hereunder or the date of such Advance
                  until paid in full at a rate of interest equal to the lesser
                  of (a) the Maximum Rate, or (b) a floating rate of interest
                  (the "Floating Rate") which is equal to 275 basis points
                  (2.75%) per annum over the Monthly Average LIBOR Rate.

         (d) Section 2.4(a) is amended by the addition of the following
         subsections (5) and (6):

                  "(5) The unpaid amount of each Advance outstanding against a
                  Commercial Mortgage Loan that is not an Aged Loan shall bear
                  interest from the date of such Advance until paid in full, at
                  a rate of interest equal to the lesser of (i) the Maximum
                  Rate, or (ii) a floating rate of interest which is equal to
                  325 basis points (3.25%) per annum over the Monthly Average
                  LIBOR Rate.

                  "(6) The unpaid amount of each Advance outstanding against an
                  Aged Loan that is a Commercial Mortgage Loan shall bear
                  interest from the date of such Advance until paid in full, at
                  a rate of interest equal to the lesser of (i) the Maximum
                  Rate, or (ii) a floating rate of interest which is equal to
                  375 basis points (3.75%) per annum over the Monthly Average
                  LIBOR Rate."

         (e) Section 2.5(a) is deleted in its entirety, and the following is
         substituted therefor:

                  "(a) The outstanding unpaid principal amount of all Advances
                  shall be payable in full upon June 14, 1999."

         (f) Section 2.5(c) of the Credit Agreement is hereby deleted in its
         entirety, and the following is substituted therefor:

         "2.5. Principal Payments.

                           (c) The Company shall be obligated to pay to the
                  Lender, without the necessity of prior demand or notice from
                  the Lender, and the Company authorizes the Lender to charge
                  the Funding Account or any accounts of the Company in Lender's
                  possession for the amount of any outstanding Advance against a
                  specific Residential Construction 


--------------------------------------------------------------------------------

                                                                          Page 8
<PAGE>   9

                  Loan, Residential A&D Loan, Aged Loan, Consumer Construction
                  Loan, Consumer Lot Loan, or Commercial Mortgage Loan, as the
                  case may be, upon the earliest occurrence of any of the
                  following events:

                           "(1) Any Residential Construction Loan that has been
                           included in Collateral for more than three hundred
                           sixty (360) days; except for any Residential
                           Construction Loan that continued to be an Eligible
                           Construction Loan at the end of such period and in
                           such event shall automatically be deemed an Aged
                           Loan;

                           "(2) Any Residential Construction Loan for Model
                           Homes has been included in Collateral for more than
                           six hundred thirty (630) days; except for any
                           Residential Construction Loan for any Model Home that
                           continues to be an Eligible Construction Loan at the
                           end of such period and in such event shall
                           automatically be deemed an Aged Loan;

                           (3) Any Residential A&D Loan has been included in
                           Collateral for more than six hundred thirty (630)
                           days; except for any such Residential A&D Loan that
                           continues to be an Eligible Construction Loan at the
                           end of such period and in such event shall
                           automatically be deemed an Aged Loan;

                           (4) Any Consumer Construction Loan or Consumer Lot
                           Loan has been included in Collateral for more than
                           five hundred forty (540) days;

                           "(5) Any Commercial Mortgage Loan has been included
                           in Collateral for more than the three hundred
                           sixty-five (365) days; except for any Commercial
                           Mortgage Loan that continues to be an Eligible
                           Commercial Loan at the end of such period and in such
                           event shall automatically be deemed an Aged Mortgage
                           Loan;

                           "(6) Any Aged Loan has been included in Collateral
                           (as an Aged Loan) for more than ninety (90) days,
                           unless such Aged Loan is a Residential A&D Loan or a
                           Residential Construction Loan for a Model Home, in
                           which case such Aged Loan has been included in the
                           Collateral (as an Aged Loan) for more than one
                           hundred eighty (180) days;

                           "(7) Such Residential Construction Loan, Residential
                           A&D Loan, Aged Loan, Consumer Construction Loan,
                           Consumer Lot Loan, or Commercial Mortgage Loan, is
                           not or ceases to be an Eligible Construction Loan or
                           Eligible Commercial Loan;

                           "(8) Upon receipt by Company of payment by the
                           Builder of such Residential Construction Loan,
                           Residential A&D Loan or Aged Loan in full;


--------------------------------------------------------------------------------

                                                                          Page 9
<PAGE>   10

                           "(9) Upon receipt by Company of payment by the
                           Borrower of any such Consumer Construction Loan,
                           Consumer Lot Loan, Commercial Mortgage Loan, or Aged
                           Loan, in full;

                           "(10) Notwithstanding the foregoing, any Aged Loan
                           that is an Acquired Loan may remain in the Collateral
                           for a period greater than 450 days but no more than
                           720 days, subject to the provisions of Section
                           2.1(c)(7) hereof. All amounts advanced against such
                           Aged Loans that are Acquired Loans shall be due and
                           payable when such Aged Loans have been included in
                           the Collateral for more than 720 days.

         (g) Section 2.9 is deleted in its entirety, and the following is
         substituted therefor:

                  "2.9 Commitment Fee. In consideration of Lender's agreement to
                  make Advances available to Company under the Commitment and to
                  extend the term of the Credit Agreement, subject to the terms
                  of this Agreement, Company shall pay to Lender a commitment
                  fee equal to $100,000 per annum, or $50,000 for six months
                  (the "Commitment Fee"). The Commitment Fee shall be due in two
                  (2) equal quarterly installments of $25,000 each. The first
                  installment of $25,000 shall be due and payable on the
                  execution date hereof and a like installment of $25,000.00
                  shall be due and payable on April 1, 1999. The Commitment Fee
                  shall be deemed fully earned and non-refundable upon the
                  execution and delivery of this Agreement by the parties,
                  notwithstanding the Commitment is never fully funded during
                  the term of this Agreement.

         (h) Sections 3.1(a) is deleted in its entirety, and the following is
         substituted therefor:

                  "(a) All Residential Construction Loans and all Commercial
                  Mortgage Loans and all Residential A&D Loans, including all
                  Commercial Notes, Construction Notes, Construction Loan
                  Agreements, Deeds of Trust, and all other Construction Loan
                  Documents or Commercial Loan Documents, as applicable,
                  evidencing and/or securing such Residential Construction
                  Loans, Residential A&D Loans or Commercial Mortgage Loans in
                  respect of which an Advance has been made by the Lender
                  hereunder."

         (i) Section 3.2 is deleted in its entirety, and the following is
         substituted therefor:

                  "3.2 Right of Redemption from Pledge. So long as no Event of
                  Default has occurred, the Company may redeem a Residential
                  Construction Loan, Residential A&D Loan, Aged Loan, Consumer
                  Construction Loan, Consumer Lot Loan or Commercial Mortgage
                  Loan by notifying the Lender of its intention to redeem such
                  Residential Construction Loan, Residential A&D Loan, Aged
                  Loan, Consumer Loan, Consumer Lot Loan, or Commercial Mortgage
                  Loan from pledge and by paying to Lender, for application to
                  prepayment of the principal balance of the Note, an amount


--------------------------------------------------------------------------------

                                                                         Page 10
<PAGE>   11

                  equal to the amount of all Advances outstanding with respect
                  to or relating to such Residential Construction Loan,
                  Residential A&D Loan, Aged Loan, Consumer Construction Loan,
                  Consumer Lot Loan, or Commercial Mortgage Loan."

         (j) Sections 4.2(d), 5.13, 5.18, and 6.10 are deleted in their
         entirety, and the following are substituted therefor:

                  "4.2(d) Lender shall not be obligated to fund all or any
                  portion of any Advance to be used to fund any Residential
                  Construction Loan, Residential A&D Loan, Consumer Construction
                  Loan, Consumer Lot Loan, or Commercial Mortgage Loan, unless
                  such Residential Construction Loan, Residential A&D Loan,
                  Consumer Construction Loan, or Consumer Lot Loan is an
                  Eligible Construction Loan or such Commercial Mortgage Loan is
                  an Eligible Commercial Loan."

                  "5.13 Direct Benefit From Loans. The Company has received, or,
                  upon the execution and funding thereof, will receive (a)
                  direct benefit from the making and execution of this Agreement
                  and the other Loan Documents to which it is a party, and (b)
                  fair and independent consideration for the entry into, and
                  performance of, this Agreement and the other Loan Documents to
                  which it is a party. Contemporaneously with the disbursements
                  of each Advance by the Lender to the Company, all such
                  proceeds will be used to fund or purchase and/or fund
                  Residential Construction Loans, Residential A&D Loans,
                  Consumer Construction Loans, Consumer Lot Loans, or Commercial
                  Mortgage Loans in accordance with the applicable Request for
                  Advance and none other."

                  "5.18 Use of Proceeds; Business Loans. The Company will use
                  the proceeds of the Advances made pursuant to the Commitment
                  solely as follows, and for no other purpose: finance the
                  funding of Residential Construction Loans, Residential A&D
                  Loans, Consumer Construction Loans, Consumer Lot Loans, and
                  Commercial Mortgage Loans. All loans evidenced by the Note are
                  and shall be "business loans" as such term is used in the
                  Depository Institutions Deregulation and Monetary Control Act
                  of 1980, as amended, and such loans are for business or
                  commercial purposes and not primarily for personal, family,
                  household or agricultural use, as such terms are used or
                  defined in chapter 1D, Texas Credit Title, Regulation Z
                  promulgated by the Board of Governors of the Federal Reserve
                  System, and Titles I and V of the Consumer Credit Protection
                  Act. The provisions of the Texas Credit Title which regulate
                  revolving loans and revolving triparty accounts) shall not
                  apply to this Agreement."

                  "6.10 Use of Proceeds of Advances. Use the proceeds of each
                  Advance solely for the purpose of financing the origination,
                  purchase, and/or funding of Residential Construction Loans,
                  Residential A&D Loans, Aged Loans, Consumer Construction
                  Loans, Consumer Lot Loans, and Commercial Mortgage Loans in
                  accordance with the applicable Request for Advance, and none
                  other.


--------------------------------------------------------------------------------

                                                                         Page 11
<PAGE>   12

         (k) The Credit Agreement is amended by the addition of the following
         Sections 5.23 and 6.12:

                  "5.23 Year 2000 Review. Borrower represents and warrants to
                  the Lender that (a) it and its Subsidiaries have reviewed the
                  effect of the Year 2000 Issue on the computer software,
                  hardware, and firmware systems and equipment containing
                  embedded microchips owned or operated by or for Borrower and
                  its Subsidiaries or used or relied upon in the conduct of
                  their business (including systems and equipment supplied by
                  others or with which such computer systems of Borrower and its
                  Subsidiaries interface) and (b) the costs to Borrower and its
                  Subsidiaries of any reprogramming required as a result of the
                  Year 2000 Issue to permit the proper functioning of such
                  systems and equipment and the proper processing of data, and
                  the testing of such reprogramming, and of the reasonably
                  foreseeable consequences of the Year 2000 Issue to Borrower or
                  any of its subsidiaries (including reprogramming errors and
                  the failure of systems or equipment supplied by others), are
                  not reasonably expected to result in a Default or Event of
                  Default or to have a material adverse effect on the business,
                  assets, operations, prospects, or condition (financial or
                  otherwise) of Borrower or its Subsidiaries.

                  "6.12 Year 2000 Compliance. Borrower covenants and agrees with
                  Lender that it shall take all necessary action to complete in
                  all material respects by September 30, 1999, the reprogramming
                  of computer software, hardware, and firmware systems used or
                  relied upon in the conduct of its business (including systems
                  and equipment supplied by others or with which such systems of
                  Borrower interface) required as a result of the Year 2000
                  Issue to permit the proper functioning of such computer
                  systems and other equipment and testing of such systems and
                  equipment, as so reprogrammed. At the request of the Lender,
                  Borrower shall provide to the Lender reasonable assurance of
                  its compliance with the preceding sentence."

         (l) Section 7.4 is deleted in its entirety, and the following is
         substituted therefor:

                           "7.4 Minimum Tangible Net Worth. Permit Minimum
                           Tangible Net Worth of the Company (and its
                           Subsidiaries, on a consolidated basis) to be less
                           than SIX MILLION AND NO/100 DOLLARS ($6,000,000.00),
                           computed as of the end of each calendar month.

         (m) The promissory note ("Credit Note") dated as of December 15, 1998,
         in the original principal amount of $40,000,000, executed by Borrower
         and payable to the order of Lender, is given to Lender in replacement
         of that certain promissory note dated as of December 31, 1997, in the
         original principal amount of $75,000,000, executed by Borrower and
         payable to the order of Lender (the "Original Note"), and not in
         novation or discharge thereof. The definition of the term "Note" in the
         Credit Agreement is hereby amended to mean the Credit 


--------------------------------------------------------------------------------

                                                                         Page 12
<PAGE>   13

         Note and all renewals, extensions, modifications, increases,
         rearrangements, and replacements thereof.

         Section 3. Representations. The Company represents and warrants that
all of the representations and warranties contained in the Credit Agreement and
all instruments and documents executed pursuant thereto or contemplated thereby
are true and correct in all material respects on and as of this date.

         Section 4. Continued Force and Effect. Except as specifically amended
herein, all of the terms and conditions of the Credit Agreement and all other
Loan Documents are and remain in full force and effect in accordance with their
respective terms. All of the terms used herein have the same meanings as set out
in the Credit Agreement, unless amended hereby or unless the context clearly
requires otherwise. References in the Credit Agreement to the "Agreement," the
"Loan Agreement," "hereof," "herein" and words of similar import shall be deemed
to be references to the Credit Agreement as amended hereby. Any reference in the
other Loan Documents to the "Agreement," the "Line of Credit Agreement,"
"Warehouse Agreement," or the "Loan Agreement" shall be deemed to be references
to the Credit Agreement as amended through the date hereof. Any references in
the Credit Agreement or any of the Loan Documents to the Note or the Credit Note
shall be deemed to be references to the Credit Note.

          Section 5. Guarantor. NAB Asset Corporation joins in the execution of
this Amendment for, among other things, the purpose of ratifying its Guaranty
dated December 30, 1997 (the "Guaranty"), which guarantees the payment of the
indebtedness evidenced by the Credit Agreement and the Credit Note. GUARANTOR
(I) CONSENTS TO THE TERMS OF THIS AMENDMENT, (II) RATIFIES AND CONFIRMS THE
GUARANTY, WHICH IS IN FULL FORCE AND EFFECT IN ACCORDANCE WITH ITS TERMS, AND
(III) ACKNOWLEDGES THAT THE GUARANTY IS NOT SUBJECT TO ANY CLAIMS, OFFSETS,
DEFENSES, OR COUNTERCLAIMS OF ANY NATURE WHATSOEVER.

         Section 6. Representations and Release of Claims. Except as otherwise
specified herein, the terms and provisions hereof shall in no manner impair,
limit, restrict or otherwise affect the obligations of the Company, Guarantor,
or any third party to Lender, as evidenced by the Loan Documents. The Company
and Guarantor hereby acknowledge, agree, and represent that (i) the Company is
indebted to Lender pursuant to the terms of the Credit Note; (ii) the liens,
security interests and assignments created and evidenced by the Loan Documents
are, respectively, first, prior, valid and subsisting liens, security interests
and assignments against the Collateral and secure all indebtedness and
obligations of the Company to Lender under the Credit Note, the Credit
Agreement, and all other Loan Documents, as modified herein; (iii) there are no
claims or offsets against, or defenses or counterclaims to, the terms or
provisions of the Loan Documents, and the other obligations created or evidenced
by the Loan Documents; (iv) neither the Company nor the Guarantor has any
claims, offsets, defenses or counterclaims arising from any of the Lender's acts
or omissions with respect to the Loan Documents, or the Lender's performance
under the Loan Documents; (v) the representations and warranties contained in
the Loan Documents are true and correct representations and warranties of the
Company, as of the date hereof; (vi) the Company promises to pay to the order of
Lender the indebtedness evidenced by the Credit Note according to 


--------------------------------------------------------------------------------

                                                                         Page 13
<PAGE>   14

the terms thereof; and (vii) the Company is not in default and no event has
occurred which, with the passage of time, giving of notice, or both, would
constitute a default by the Company of the Company's obligations under the terms
and provisions of the Loan Documents. In consideration of the modification of
certain provisions of the Loan Documents, all as herein provided, and the other
benefits received by the Company hereunder, the Company and Guarantor hereby
RELEASE, RELINQUISH and forever DISCHARGE Lender, its predecessors, successors,
assigns, shareholders, principals, parents, subsidiaries, agents, officers,
directors, employees, attorneys and representatives (collectively, the "Lender
Released Parties"), of and from any and all claims, demands, actions and causes
of action of any and every kind or character, whether known or unknown, present
or future, which the Company has, or may have against Lender Released Parties,
arising out of or with respect to any and all transactions relating to the
Credit Agreement, the Credit Note, the Original Note, the Guaranty, and the
other Loan Documents occurring prior to the date hereof, including any other
loss, expense and/or detriment, of any kind or character, growing out of or in
any way connected with or in any way resulting from the acts, actions or
omissions of the Lender Released Parties, and including any loss, cost or damage
in connection with any breach of fiduciary duty, breach of any duty of fair
dealing, breach of competence, breach of funding commitment, undue influence,
duress, economic coercion, conflict of interest, negligence, bad faith,
malpractice, violations of the Racketeer Influence and Corrupt Organizations
Act, intentional or negligent infliction of emotional or mental distress,
tortious interference with corporate governments or prospective business
advantage, tortious interference with contractual relations, breach of contract,
deceptive trade practices, libel, slander, conspiracy, the charging, contracting
for, taking, reserving, collecting or receiving of interest in excess of the
highest lawful rate applicable to the Loan Documents (i.e., usury), any
violations of federal or state law, any violations of federal or state banking
rules, laws or regulations, including, but not limited to, any violations of
Regulation B, Equal Credit Opportunity, bank tying act claims, any violation of
the Texas Free Enterprise Antitrust Act or any violation of federal antitrust
acts.

         Section 7. Severability. In the event any one or more provisions
contained in the Credit Agreement, this Amendment, or any of the Loan Documents
should be held to be invalid, illegal or unenforceable in any respect, the
validity, enforceability and legality of the remaining provisions contained
herein and therein shall not be affected in any way or impaired thereby and
shall be enforceable in accordance with their respective terms.

         Section 8. Expenses. The Company agrees to pay all out-of-pocket costs
and expenses (including reasonable fees and expenses of legal counsel) of Lender
in connection with the preparation, operation, administration and enforcement of
this Amendment.

         Section 9. Acknowledgment. Except as amended hereby, the Company and
Guarantor ratify and confirm that the Loan Documents are and remain in full
force and effect in accordance with their respective terms and that all
Collateral is unimpaired by this Amendment and secures the payment and
performance of all indebtedness and obligations of the Company under the Credit
Note, the Credit Agreement, and all other Loan Documents, as modified hereby.
The undersigned 


--------------------------------------------------------------------------------

                                                                         Page 14
<PAGE>   15

officer of the Company executing this Amendment represents and warrants that he
has full power and authority to execute and deliver this Amendment on behalf of
the Company. The undersigned officer of the Company represents and warrants that
his execution and delivery of this Amendment has been duly authorized, and that
the resolutions and affidavits previously delivered to Lender, in connection
with the execution and delivery of the Credit Agreement, are and remain in full
force and effect and have not been altered, amended or repealed in anywise.

         Section 10. No Waiver. The Company and Guarantor agree that no Event of
Default and no Default has been waived or remedied by the execution of this
Amendment by Lender, and any such Default or Event of Default heretofore arising
and currently continuing shall continue after the execution and delivery hereof.

         Section 11. Governing Law. This Amendment shall be governed by and
construed in accordance with the laws of the State of Texas and, to the extent
applicable, by federal law.

         Section 12. Counterparts. This Amendment may be executed in any number
of counterparts and all of such counterparts taken together shall be deemed to
constitute one and the same instrument.

         SECTION 13. NO ORAL AGREEMENTS. THIS WRITTEN AMENDMENT, THE CREDIT
AGREEMENT, THE CREDIT NOTE, THE GUARANTY, AND THE OTHER LOAN DOCUMENTS, ALL AS
MODIFIED HEREBY, REPRESENT THE FINAL AGREEMENT BETWEEN THE PARTIES AND MAY NOT
BE CONTRADICTED BY EVIDENCE OF PRIOR, CONTEMPORANEOUS OR ORAL AGREEMENTS OF THE
PARTIES.

         THERE ARE NO UNWRITTEN ORAL AGREEMENTS BETWEEN THE PARTIES.

         EXECUTED and effective as of the dates first written above.

COMPANY:                                     GUARANTOR:
--------                                     ----------

CONSTRUCTION PORTFOLIO
FUNDING, INC.,                               NAB ASSET CORPORATION,
a Texas corporation                          a Texas corporation


                                             By: /s/ Alan Ferree
By: /s/ James R. Reynolds                    Name: Alan Ferree
Name: James R. Reynolds                      Title: Senior Vice-President
Title: President


                                             LENDER:

                                             BANK UNITED,
                                             a federal savings bank


                                             By: /s/ Deborah A. Bourque
                                             Name: Deborah A. Bourque
                                             Title: Regional Director


--------------------------------------------------------------------------------

                                                                         Page 15