A board may expend surplus funds under its control, not necessary for use to maintain the law library, to acquire or lease real property and erect thereon a library building to house the law library. In the alternative, a board of law library trustees may appropriate from the surplus funds so much as in the discretion of the board may be necessary to obtain adequate quarters for the law library in any building hereafter erected by the board of supervisors of the county in which the law library is maintained. The moneys so appropriated shall not be more than the proportion of the total cost of the building which the space allotted to the law library bears to the total usable space in the building. The moneys so appropriated may be transferred to the board of supervisors of the county for use in erecting the
building, or may be paid directly on contracts for the erection thereof made by the board of supervisors.