Contracts for the construction of local system road projects must be advertised and let by the board of supervisors of the county in the manner required by law. Before advertising for bids, plans and specifications covering the proposed work shall be prepared by the county engineer and filed in the chancery clerk's office of the county. Copies of the plans and specifications shall be subject to inspection during regular office hours and shall be made available to all prospective bidders upon such terms and conditions as may be required by the board and its county engineer.