Belfries, church spires, cupolas, penthouses and domes which are not used for human occupancy; nor to chimneys, ventilators, skylights, solar collectors, green roof systems, water tanks and necessary mechanical appurtenances usually carried above the roof level; nor to flagpoles, monuments, radio and television antennas or towers and similar structures. Such features, however, shall be erected only to such height as is necessary to accomplish the purpose for which they are intended. No advertising device of any kind whatsoever shall be inscribed upon or attached to that part of any chimney, tower, tank or other structure which extends above the roof limitations.