You would have seen overlapping elements in roofs. These are roof shingles. For better water proof results double layers are also used. Shingles can be made of different materials. Different materials give different look to your roof. The materials could be asphalt, ceramic, asbestos cement, slate, and wood. Some of these are not fire proof and hence fiberglass based asphalt shingles are increasingly used in the United States.
Boards of size 1 x 6 inches are used in the roof and the wooden shingles are nailed to these boards. It is done so, so that there is air circulation below the wooden shingles and this increases the durability and the shingles may not become soggy. Shingles can also be fixed on existing roof materials if any. Depending on the climate of your locality the durability of the shingles may vary. Look for any damaged shingles after a rough weather and fix it immediately.