I consider terra cotta(barrel) tiles decorative. They virtually last forever although most places will say 50+ years. They need to be installed over a base that is waterproof and will last equally long. Because of their weight, roofs need to be built to support the extra load. I've seen 50+ year old roofs stripped of the tiles, a new base applied and the old tiles put back down. You should be able to find someone to inspect them for you by asking around for the specialty roof installers. They would do things like tile, concrete, slate-- maybe even shakes.