A board of law library trustees may enter into an agreement with a county for the joint exercise of powers pursuant to Chapter 5 (commencing with Section 6500) of Division 7 of Title 1 of the Government Code for the purpose of constructing a building or buildings to house the law library and court or county facilities, without limitation as to the number of courtrooms such building or buildings may contain, and may lease from any authority created pursuant to such agreement the space required for law library purposes.