The “home for the aged fund” may be used for the purposes as in this act provided and any time after the first levy has been made, if there be sufficient funds obtained, the county commissioners may proceed to acquire the site by gift or purchase and let the contract for such building or buildings. No building or buildings shall be erected or constructed until the plans and specifications have been made therefor and adopted by the board of county commissioners, and bid, advertised for, according to law, for other county public buildings.