Slate roofs are done with roofing tiles made from slate which is an ancient sedimentary rock made up mainly from clay and other volcanic materials, and compounded in the earth by pressure and heat. Slate is a very common roofing material because it is very strong and also waterproof. It is very popular because it can be easily shaped into the rectangles that we see on the roofs of today. During the manufacture of roofing slates, big pieces of slate rock are broken into small sheets quite easily. Again this makes slate an ideal material for roofing. Slate can last a very long time because slate is a very hardwearing material. The disadvantage of slate as a roofing material is that it is very expensive to buy and replace. In some areas roofs have to be kept maintained with specific types of slate in order to satisfy planning laws and keep the architectural character of buildings uniform in certain areas. Finding specific types of slate in such cases can be very difficult and there are few roofing contractors which undertake this kind of work.