((a)) ** .—** When the Administrator of General Services decides it to be necessary, the Administrator may employ, by contract or otherwise, without regard to chapters 33 and 51 and subchapter III of chapter 53 of title 5, civil service rules and regulations, or section 6101(b) to (d) of title 41, the services of established architectural or engineering corporations, firms, or individuals, to the extent the Administrator may require those services for any public building authorized to be constructed or altered under this chapter.

((b)) ** .—** A corporation, firm, or individual shall not be employed under authority of subsection (a) on a permanent basis.

((c)) ** .—** Notwithstanding any other provision of this section, the Administrator is responsible for all construction authorized by this chapter, including the interpretation of construction contracts, approval of material and workmanship supplied under a construction contract, approval of changes in the construction contract, certification of vouchers for payments due the contractor, and final settlement of the contract.