<PAGE>

                                                                   EXHIBIT 10.28

                       FIRST AMENDMENT TO CONTRACT OF SALE

        This FIRST AMENDMENT TO CONTRACT OF SALE (this "Amendment") is made and
entered into effective as of the ____ day of June, 2003 (the "Effective Date"),
by and among VORTISCH HOLDINGS, L.P., a Texas limited partnership ("Seller"),
CANTEX REALTIES, INC., a Texas corporation ("Cantex"), and REALTY AMERICA GROUP
I, LP, a Texas limited partnership ("Original Purchaser"), and REALTY AMERICA
GROUP (4245 CENTRAL), LP, a Texas limited partnership ("Purchaser").

                             PRELIMINARY STATEMENTS:

        The following preliminary statements are a material part of this
Amendment:

        A.      Seller, Cantex and Original Purchaser, as predecessor in
interest to Purchaser made and entered into that certain Contract of Sale, dated
effective April 16, 2004 (the "Contract"), with respect to certain real property
located on that certain tract or parcel of land situated in the City of Dallas,
Dallas County, Texas, which is more particularly described in the Contract (the
"Property").

        B.      Seller, Cantex, Original Purchaser, and Purchaser desire to
amend the Contract as set forth below.

                                   AGREEMENTS:

        NOW THEREFORE, in consideration of the agreements to sell and purchase
the Property and the mutual covenants and agreements contained in this Amendment
and in the Contract, and other good and valuable consideration, the receipt and
adequacy of which are hereby acknowledged, Seller, Original Purchaser and
Purchaser hereby agree as follows:

1.      EFFECTIVE DATE OF CONTRACT. Article 16 of the Contract is hereby amended
        to reflect an effective date of April 19, 2004, and the deadline for
        submitting a fully executed Contract to the Title Company shall also be
        amended to April 19, 2004. Any and all dates in the Contract shall be
        determined based upon the fact that the Contract's effective date is
        April 19, 2004.

2.      ASSIGNMENT AND ASSUMPTION OF CONTRACT. Pursuant to the provisions of
        Article 15.7, Seller and Cantex hereby acknowledge and consent to the
        assignment of the Contract from Original Purchaser to Purchaser. Any
        reference in the Contract to Purchaser shall hereinafter refer to Realty
        America Group (4245 Central), LP. Purchaser hereby assumes the rights,
        titles and obligations of Original Purchaser, and Original Purchaser is
        hereby forever released from any and all liability and/or obligations
        pursuant to the Contract.

3.      CAPITALIZED TERMS. Capitalized terms used but not defined in this
        Amendment shall have the same meaning as those in the Contract, unless
        otherwise noted herein.

<PAGE>

4.      RATIFICATION OF CONTRACT. Except as specifically modified by this
        Amendment, all of the other terms and provisions of the Contract shall
        remain in full force and effect, and are hereby ratified and confirmed
        by Seller, Cantex and Purchaser. Notwithstanding the foregoing, in the
        event there is any conflict between the terms and provisions of the
        Contract and this Amendment, the terms and provisions of this Amendment
        shall control.

5.      REPRESENTATIONS AND WARRANTIES. Seller, Cantex, Original Purchaser and
        Purchaser represent and warrant to each other respectively that they
        have the requisite power and authority to enter into this Amendment;
        that all necessary and appropriate approvals, authorizations and other
        steps have been taken to effect the legality of this Amendment; that the
        signatories executing this Amendment are authorized to do so on behalf
        of Seller, Original Purchaser and Purchaser; and that this Amendment is
        valid and binding upon and enforceable against Seller, Cantex, Original
        Purchaser and Purchaser.

6.      COUNTERPARTS. This Amendment may be executed in any number of
        counterparts, each of which shall be deemed an original. Facsimile
        copies of the signature pages to this Amendment shall be deemed to be
        originals for all purposes of this Amendment.

8.      FINAL AGREEMENT. This Amendment and the Contract cover in full, each and
        every final agreement of every kind or nature whatsoever between Seller,
        Cantex, Original Purchaser and Purchaser concerning the Property, and
        all preliminary negotiations and agreements whatsoever of every kind or
        nature are merged into this Amendment and the Contract. This Amendment
        and the Contract cannot be changed or modified in any manner other than
        by written amendment or modification executed by Seller, Cantex and
        Purchaser.

9.      SUCCESSORS AND ASSIGNS. This Amendment is binding upon and inures to the
        benefit of Seller, Cantex and Purchaser and their respective successors
        and assigns.

<PAGE>

        IN WITNESS WHEREOF, Seller, Cantex, Original Purchaser, and Purchaser
have caused this Amendment to be duly executed as of the Effective Date.

                                SELLER:

                                VORTISCH HOLDINGS, L.P.,
                                a Texas limited partnership

                                By: VORTISCH INVESTMENTS, INC.,
                                    a Delaware corporation
                                    its general partner

                                    By:
                                             -----------------------------------
                                             Hermann Vortisch
                                             President

                                    Date of Signature: April ____, 2004



                                ORIGINAL PURCHASER:

                                REALTY AMERICA GROUP I, LP,
                                a Texas limited partnership

                                By: REALTY AMERICA GROUP, LLC,
                                    a Texas limited liability company
                                    its general partner

                                    By:
                                             -----------------------------------
                                             Webb M. Sowden, III
                                             Member

                                    Date of Signature: April  ____, 2004

<PAGE>

                                PURCHASER:

                                REALTY AMERICA GROUP (4245 CENTRAL), LP,
                                a Texas limited partnership

                                By: REALTY AMERICA GROUP INVESTMENTS, LLC,
                                    a Texas limited liability company
                                    its general partner

                                    By:
                                             -----------------------------------
                                             Webb M. Sowden, III
                                             Member

                                    Date of Signature: April  ____, 2004

                                CANTEX:

                                CANTEX REALTIES, INC.,
                                a Texas corporation


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

                                Date of Signature: April  ____, 2004