(a) Certificate and adjustment. No loan shall be insured unless a certification of actual cost is made by the contractor.

(b) Cost computation. The term actual cost of the improvements shall mean the cost to the borrower of the improvements, after deducting the amount of any kickbacks, rebates, or trade discount received in connection with the improvements, and including the amounts paid under any contract for the improvements, labor, materials, and for any other items of expense approved by the Commissioner.

(c) Statement of facts. Any agreement, undertaking, statement or certification required in connection with cost certification shall specifically state that it has been made, presented and delivered for the purpose of influencing an official action of the Commissioner and may be relied upon as a true statement of the facts contained therein.

(d) Incontestability. Upon the Commissioner's approval of the cost certification, such certification shall be final and incontestable except for fraud or material misrepresentation on the part of the borrower.

(e) Records. The borrower shall keep and maintain adequate records of all costs of any construction improvements or other cost items not representing work under the general contract and shall require the builder to keep similar records and, upon request by the Commissioner, shall make available for examination such records, including any collateral agreements.