The board of county commissioners may provide for the purchase, erection, repair, and maintenance of the courthouse, hospitals, jails, and other necessary buildings within and for the county. It may purchase the sites for such county buildings if necessary and may make contracts on behalf of the county for the building, repairing, and maintaining thereof if the expenditures therefor are not greater than can be paid out of the revenue of the county for the current year. The board shall have the entire supervision of the construction of such buildings.