EXHIBIT 10.93



December 24,1998


To:         Lundgren Bros. Construction, Inc.
            935 East Wayzata Boulevard
            Wayzata, Minnesota  55391

                                                                FOURTH AMENDMENT
                                                             TO LETTER AGREEMENT
Ladies and Gentlemen:

            This fourth amendment to letter agreement (the "Amendment") is being
executed in order to amend certain of the terms and conditions contained in that
certain letter agreement dated March 21, 1996, as previously amended by
Amendment to Letter Agreement dated March 21, 1997, by Second Amendment to
Letter Agreement dated March 21, 1998, and by Third Amendment to Letter
Agreement dated April 29, 1998 (hereinafter collectively referred to as the
"Letter Agreement") between Lundgren Bros. Construction, Inc., a Minnesota
corporation (the "Borrower"), and U.S. Bank National Association, a national
banking association, formerly known as First Bank National Association (the
"Bank"). In consideration of the mutual agreements set forth herein, and for
other good and valuable consideration, the receipt and sufficiency of which is
hereby acknowledged by the parties, the Borrower and the Bank agree to further
amend the Letter Agreement as follows:

            (a)   Paragraph 1 of the Letter Agreement, as previously amended, is
                  hereby deleted in its entirety and the following paragraph
                  inserted in lieu thereof effective as of December 24, 1998:

                              "1. Subject to the provisions of this letter
                        agreement, at the Borrower's request, the Bank shall
                        make loans to the Borrower during the period from the
                        date of this letter agreement to May 31, 2000 in an
                        aggregate amount not exceeding $1,500,000.00 at any time
                        outstanding (the "Line of Credit"). The Line of Credit
                        is a revolving line of credit, and the Borrower may
                        borrow, prepay and reborrow under the Line of Credit.
                        The Borrower's obligation to repay such loans and to pay
                        interest and other charges, fees and expenses thereon is
                        evidenced by the Borrower's Fourth Amendment and
                        Restatement of Promissory Note dated as of December 23,
                        1998, payable to the order of the Bank in the principal
                        amount of $1,500,000.00 (together with any additional
                        amendments, extensions, renewals and replacements
                        thereof, called the "Revolving Note"). The Bank shall
                        have no obligation to make any such loan after the




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                        occurrence of any default or event of default under the
                        Revolving Note or any other agreement of the Borrower
                        with the Bank, or any other event that would accelerate
                        or allow the Bank to accelerate payment of the Revolving
                        Note. The Borrower shall use all proceeds of such loans
                        solely for working capital of the Borrower."

            (b)   Paragraph 4(a) of the letter agreement is hereby deleted in
                  its entirety and the following paragraph inserted in lieu
                  thereof effective as of December 24, 1998:

                        "Borrowing Base" shall mean:

                              (a) during the period from the date of this letter
                              agreement through May 31, 2000, the sum of (i)
                              $300,000.00, plus (ii) the aggregate fair market
                              value of the Borrower's investments which the
                              Bank, in its sole discretion, shall deem
                              acceptable, and in which the Bank shall have a
                              perfected security interest constituting a first
                              lien in form and substance acceptable to the
                              Bank."

            (c)   Exhibit A attached to the Letter Agreement is hereby deleted
                  in its entirety and replaced with Exhibit A attached hereto
                  and made a part hereof.

            (d)   Upon the execution and delivery by Borrower to Lender of this
                  Amendment and the Fourth Amendment and Restatement of
                  Promissory Note dated December 23, 1998, Lender agrees to
                  release Edmund Lundgren, Allan Lundgren, Peter Pflaum and
                  Gerald Lundgren (the "Guarantors" or individually "Guarantor")
                  from all of their obligations under that certain Guaranty
                  given by each Guarantor in favor of First Bank National
                  Association, each such Guaranty dated March 21, 1996.

            (e)   Except as herein expressly modified, all of the terms and
                  conditions of the Letter Agreement shall remain in full force
                  and effect.

                              Sincerely,

                              U.S. BANK NATIONAL ASSOCIATION,
                              a national banking association, formerly known as
                              First Bank National Association


                              By:_______________________________________

                              Its:_______________________________________



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            Lundgren Bros. Construction, Inc. agrees to this Fourth Amendment to
Letter Agreement.

Executed as of December __, 1998.

LUNDGREN BROS. CONSTRUCTION, INC.,
a Minnesota corporation


By:____________________________________

Its:____________________________________



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                                    EXHIBIT A

                        LUNDGREN BROS. CONSTRUCTION, INC.

                             BORROWER'S CERTIFICATE


            I, _______________________, the chief financial officer of Lundgren
Bros. Construction, Inc., a Minnesota corporation (the "Borrower"), pursuant to
the letter agreement dated March 21, 1996, as modified by amendments to letter
agreement dated March 21, 1997, March 21, 1998, April 29, 1998 and December 23,
1998, respectively (collectively, the "Agreement"), hereby certify to U.S. Bank
National Association, formerly known as First Bank National Association (the
"Bank"):

            1.    As of the close of business on ____________, 199___ (the most
                  recent Determination Date), the aggregate fair market value of
                  the Borrower's investments in account number 000303451 at FBS
                  Investment Services, Inc. was $_______________.

            2.    As of the date of this Certificate, no event has occurred
                  which constitutes a default or an event of default under the
                  Revolving Note (as defined in the Agreement), or an event that
                  would accelerate or allow the Bank to accelerate payment of
                  the Revolving Note, or would constitute any default or event
                  of default under the Revolving Note with notice or the passage
                  of time or both.

Date of Certificate:  __________________, 19_____





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                                           Signature