Farm buildings, architectural features, etc. Barns, silos, or other farm buildings or structures on farms; to church spires, belfries, cupolas, and domes, monuments, water towers, fire and hose towers, observation towers, transmission towers, windmills, chimneys, smoke-stacks, flag poles, radio towers, mast and aerials; to parapet walls extending not more than four (4) feet above the limiting height of the building.