36 C.F.R. § 51.55
Upon substantial completion of the construction of a capital improvement in which the concessioner is to obtain a leasehold surrender interest, the concessioner must provide the Director a detailed construction report. The construction report must be supported by actual invoices of the capital improvement's construction cost together with, if requested by the Director, a written certification from a certified public accountant. The construction report must document, and any requested certification by the certified public accountant must certify, that all components of the construction cost were incurred and capitalized by the concessioner in accordance with GAAP, and that all components are eligible direct or indirect construction costs as defined in this part. Invoices for additional construction costs of elements of the project that were not completed as of the date of substantial completion may subsequently be submitted to the Director for inclusion in the project's construction cost.
36 C.F.R. § 51.55