Any city or town desiring to have a building for its use erected on land owned, or to be acquired, by it, may, as lessor, lease the land for a reasonable rental for a term of not to exceed fifty years: PROVIDED, That the city or town shall lease back the building or a portion thereof for the same term. The leases shall contain terms as agreed upon between the parties, and shall include the following provisions:

(1) No part of the cost of construction of the building shall ever be or become an obligation of the city or town.

(2) The city or town shall have a prior right to occupy any or all of the building upon payment of rental as agreed upon by the parties, which rental shall not exceed prevailing rates for comparable space.

(3) During any time that all or any portion of the building is not required for occupancy by the city or town, the lessee of the land may rent the unneeded portion to suitable tenants approved by the city or town.

(4) Upon the expiration of the lease, all buildings and improvements on the land shall become the property of the city or town.