38 U.S.C. § 8106

(a) The Secretary may carry out any construction or alteration authorized under this subchapter by contract if the Secretary considers it to be advantageous to the United States to do so. (b) (1) The Secretary may obtain, by contract or otherwise, the services of individuals who are architects or engineers and of architectural and engineering corporations and firms, to the extent that the Secretary may require such services for any medical facility authorized to be constructed or altered under this subchapter. (2) No corporation, firm, or individual may be employed under the authority of paragraph (1) of this subsection on a permanent basis. (c) Notwithstanding any other provision of this section, the Secretary shall be responsible for all construction authorized under this subchapter, including the interpretation of construction contracts, the approval of materials and workmanship supplied pursuant to a construction contract, approval of changes in the construction contract, certification of vouchers for payments due the contractor, and final settlement of the contract.