The Pierce County Executive is authorized to construct, operate, maintain and collect rentals for public parking facilities upon County-City Building property not currently devoted to assigned parking stalls. The Executive is authorized to employ or contract with independent contractors for such purposes with funds made available for that purpose in the County-City Building budget approved pursuant to that certain agreement between Pierce County and the City of Tacoma dated July 17, 1958, as the same now exists or is hereafter amended.