Church spire, belfry, cupola, dome, penthouse or ornamental tower not intended for human occupancy, nor to a monument, water tank or cooling tower, observation tower, transmission tower, fire tower, fire wall, chimney, smoke stack, steeple, conveyor, flagpole, radio or television tower, mast or aerial, ventilator, skylight, elevator or stair bulkhead, air-conditioning equipment, similar features and necessary mechanical appurtenances required to operate and maintain a building and usually carried above the roof level. Any or all of such features, in the aggregate, shall not occupy more than 10% of the area of the roof of the building, except that radio or television tower, mast or aerial shall not exceed 50 feet from ground line in all residential districts.