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                                                                   EXHIBIT 10.11


                                  July 30, 1998



Developers Diversified Realty Corporation
34555 Chagrin Boulevard
Moreland Hills, Ohio

         Re:      Voting Agreement

Ladies and Gentlemen:

                  The undersigned understands that Developers Diversified Realty
Corporation, an Ohio corporation ("DDRC"), and American Industrial Properties
REIT, a Texas real estate investment trust ("AIP"), are entering into a Share
Purchase Agreement to be dated on or about the date hereof (the "Purchase
Agreement"), and, together with DDR Office Flex Corporation, a Delaware
corporation, a Merger Agreement to be dated on or about the date hereof (the
"Merger Agreement" and, together with the Purchase Agreement, the "Agreements"),
providing for, among other things, the purchase of common shares, $.10 par value
per share, of AIP by DDRC (the "Share Purchase"). Under the rules of the New
York Stock Exchange, consummation of the Share Purchase will require the
approval of the shareholders of AIP.

                  The undersigned is a shareholder of AIP (the "Shareholder")
and is entering into this letter agreement at your request, in exchange for good
and valuable consideration, the receipt and sufficiency of which is hereby
acknowledged, to induce you to enter into the Agreements and to consummate the
transactions contemplated thereby.

                  The Shareholder confirms its agreement with you as follows:

                  1.       The Shareholder represents and warrants that Schedule
                           I annexed hereto sets forth the shares of beneficial
                           interest of AIP of which the Shareholder or any
                           affiliate (as defined under the Securities Exchange
                           Act of 1934, as amended) of the Shareholder
                           controlled by the Shareholder (a "Controlled
                           Affiliate") is the beneficial owner (the "Shares")
                           and that the Shareholder and the Controlled
                           Affiliates are on the date hereof the lawful owners
                           of the number of Shares set forth in Schedule I, free
                           and clear of all liens, charges, encumbrances, voting
                           agreements and commitments of any kind, except as
                           disclosed in Schedule I. Except for the Shares set
                           forth in Schedule I, neither the Shareholder nor any
                           Controlled Affiliate owns or holds any rights to
                           acquire any additional shares of beneficial interest
                           of AIP (other than pursuant to options or conversion
                           rights with regard to any of the Shares, in each case
                           as disclosed in Schedule I) or any interest therein
                           or any


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Developers Diversified Realty Corporation
July 30, 1998
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                           voting rights with respect to any such additional
                           shares.

                  2.       Until the earliest date referred to in Section 12,
                           the Shareholder agrees that it will not, and will not
                           permit any Controlled Affiliate to, contract to sell,
                           sell or otherwise transfer or dispose of any of the
                           Shares or any interest therein or securities
                           convertible into shares of beneficial interest of
                           AIP, or any voting rights with respect thereto,
                           without your prior written consent.

                  3.       The Shareholder agrees that, during the term of this
                           letter agreement, neither it nor any Controlled
                           Affiliate will take any action that AIP would at that
                           time be prohibited from taking under Section 5.4 of
                           the Purchase Agreement.

                  4.       The Shareholder agrees that during the term of this
                           letter agreement (a) all of the shares of beneficial
                           interest of AIP beneficially owned by the Shareholder
                           or any Controlled Affiliate, or over which the
                           Shareholder or any Controlled Affiliate has voting
                           power or control, directly or indirectly (including
                           any such shares acquired after the date hereof) at
                           the record date for any meeting of shareholders of
                           AIP called to consider and vote on the Share Purchase
                           and the Agreements and the transactions contemplated
                           thereby or any Competing Transaction (as such term is
                           defined in the Purchase Agreement) will be voted by
                           the Shareholder or such Controlled Affiliates, or any
                           representative or proxy thereof, as applicable, in
                           favor of the approval of the Share Purchase and the
                           Agreements and the transactions contemplated thereby
                           and (b) neither the Shareholder nor any Controlled
                           Affiliate, nor any such representative or proxy, will
                           vote any such Shares in favor of any Competing
                           Transaction.

                  5.       The Shareholder agrees that the shares referred to in
                           Section 4 above that are owned at the record date for
                           any meeting of shareholders of AIP called to consider
                           and vote on the election of members of the Board of
                           Trust Managers of the Trust (the "Board") will be
                           voted by the Shareholder or any Controlled Affiliate,
                           or any representative or proxy thereof, as
                           applicable, in favor of the approval of the election
                           of the representatives of DDRC to the Board for so
                           long as DDRC has the right to nominate members of the
                           Board under the Purchase Agreement.

                  6.       The Shareholder hereby appoints Marc A. Simpson to
                           attend the special meeting of the shareholders of AIP
                           held to consider and vote on


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Developers Diversified Realty Corporation
July 30, 1998
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                           the Share Purchase and to vote the shares referred to
                           in Section 4 above, with all the power the
                           Shareholder would possess if personally present, in
                           favor of the approval of the Share Purchase, the
                           Agreements and the transactions contemplated thereby.
                           The Shareholder agrees to execute, and to cause each
                           Controlled Affiliate to execute, such proxies and
                           other instruments, and to take and to cause each
                           Controlled Affiliate to take such actions, as may be
                           necessary to cause all of those shares to be so
                           voted.

                  7.       The Shareholder has all necessary power and authority
                           to enter into this letter agreement. This letter
                           agreement is the legal, valid and binding agreement
                           of the Shareholder, and is enforceable against the
                           Shareholder in accordance with its terms, subject to
                           applicable bankruptcy, insolvency, fraudulent
                           conveyance, reorganization, moratorium and similar
                           laws affecting creditors' rights and remedies
                           generally and to general principles of equity. This
                           letter agreement shall inure to the benefit of the
                           parties hereto and the successors and assigns of
                           DDRC.

                  8.       The Shareholder agrees that damages are an inadequate
                           remedy for the breach by Shareholder of any term or
                           condition of this letter agreement and that you shall
                           be entitled to a temporary restraining order and
                           preliminary and permanent injunctive relief in order
                           to enforce our agreements herein.

                  9.       Except to the extent that the laws of the
                           jurisdiction of organization of any party hereto, or
                           any other jurisdiction, are mandatorily applicable to
                           matters arising under or in connection with this
                           letter agreement, this letter agreement shall be
                           governed by the laws of the State of Ohio. All
                           actions and proceedings arising out of or relating to
                           this letter agreement shall be heard and determined
                           in any United States District Court sitting in the
                           Northern District of Ohio.

                  10.      Each of the parties hereto irrevocably submits to the
                           exclusive jurisdiction of any United States District
                           Court located in the Northern District of Ohio, for
                           the purpose of any action or proceeding arising out
                           of or relating to this letter agreement and each of
                           the parties hereto irrevocably agrees that all claims
                           in respect of such action or proceeding may be heard
                           and determined exclusively in any federal court
                           sitting in the Northern District of Ohio. Each of the
                           parties hereto agrees that a final judgment in any
                           action or proceeding shall be conclusive and may


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Developers Diversified Realty Corporation
July 30, 1998
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                           be enforced in other jurisdictions by suit on the
                           judgment or in any other manner provided by law.

                  The Shareholder hereby irrevocably appoints Jones, Day, Reavis
& Pogue, Cleveland, Ohio, as its lawful agent in and for the State of Ohio, for
and in its behalf, to accept and acknowledge service of, and upon whom may be
served, all necessary processes in any action, suit, or proceeding arising under
this Agreement that may be had or brought against it in any federal court in the
Northern District of Ohio, such service of process or notice, or the acceptance
thereof by said agent endorsed thereon, to have the same force and effect as if
served upon the Shareholder, provided that any such process or notice that may
be so served shall include a conspicuous statement to the effect that is to be
forwarded immediately to USAA Real Estate Company, 9830 Colonnade Boulevard,
Suite 600, San Antonio, Texas 78230-2239, Attention: Legal Counsel (with a copy
to Patricia J. Villareal, Jones, Day, Reavis & Pogue, 2001 Ross Avenue, Suite
2300, Dallas, Texas 75201). Nothing in this Section 10 shall affect the right of
any party hereto to serve legal process in any other manner permitted by law.
Shareholder hereby waives all defenses of improper venue and forum non
conveniens with respect to any action, suit, or proceeding brought in the any
United States District Court located in the Northern District of Ohio and
arising under this letter agreement.

                  11.      This letter agreement constitutes the entire
                           agreement between the parties hereto with respect to
                           the matters covered hereby and supersedes all prior
                           agreements, understandings or representations between
                           the parties, written or oral, with respect to the
                           subject matter hereof.

                  12.      This letter agreement and the proxy granted pursuant
                           to Section 6 hereof shall become effective upon the
                           execution and delivery of the Agreements by the
                           respective parties thereto. Except as otherwise
                           provided herein, this letter agreement and the proxy
                           granted pursuant to Section 6 hereof shall terminate
                           automatically, without the need for any notice or
                           other action by either party, upon the earliest of
                           (i) the date on which the Purchase Agreement and the
                           Merger Agreement are terminated, (ii) the Second
                           Closing Date, as defined in the Purchase Agreement,
                           and (iii) the date that is 240 days after the date
                           hereof.

                  13.      Each of the parties hereto intends that AIP shall be
                           a third party beneficiary of this letter agreement,
                           and shall be entitled to the benefits hereof and
                           shall have the ability to enforce the rights granted
                           to DDRC herein as fully as if it were a signatory of
                           this letter agreement.

                  14.      Notwithstanding anything to the contrary contained
                           herein, neither AIP nor any representative of the
                           Shareholder serving on the Board of Trust Managers of
                           AIP shall be deemed to be a Controlled Affiliate.



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Developers Diversified Realty Corporation
July 30, 1998
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                  Please confirm that the foregoing correctly states the
understanding between us by signing and returning to me a counterpart hereof.

                                            USAA Real Estate Company



                                            By: /s/ T. Patrick Duncan
                                                --------------------------------
                                            Name: T. Patrick Duncan
                                                  ------------------------------
                                            Title: SVP Operations & Finance
                                                   -----------------------------



Confirmed on the date
first above written

Developers Diversified Realty Corporation


By: /s/ Scott A. Wolstein
    -------------------------------------
Name: Scott A. Wolstein
      -----------------------------------
Title: President
       ----------------------------------




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                                   Schedule I

                   Ownership of Shares of Beneficial Interest


Owned Beneficially (including Options to Purchase Shares)


<TABLE>
<CAPTION>
                                            Shares             Shares
                                           Owned of          Subject to            Total
                                            Record            Options              Shares
                                           ---------         ----------           ---------
<S>                                        <C>                  <C>               <C>      
USAA Real Estate Company                   1,674,086            6,000             1,680,086
</TABLE>