The township board of the township may lease for purposes other than the parking of automobiles, upon such terms and for such periods as it shall deem advisable, any portion of the ground and basement floor space in any structure acquired hereunder, but not to exceed 25 per centum of the total floor area of the entire structure, if it shall deem such leasing to be beneficial in connection with the acquirement and/or operation of such facilities. If a structure is designed for the parking of automobiles on the roof, such roof area shall be considered as a part of the floor area of the structure. The income from any such lease shall be deemed a part of the revenues of the facilities: Provided, however, That no business involving the servicing, repairing or the furnishing of supplies for motor vehicles other than the parking of such vehicles and the delivery thereof shall be dispensed or furnished at or in connection with any township parking facility.