A structure's interior must be protected from rain and snow. Roof cladding is waterproof and denies moisture from absorbing into the structural sheathing.
Asphalt shingles and rolled roofing accomplish this by overlapping, like a fish's scales. Rubber roofing and standing seam metal roofs do this by creating a continuous waterproof sheet across the whole of the roof plane.
Roof cladding must protect from and resist damage by winds. Areas prone to hurricanes and tornadoes have building codes that require roofs be well fastened to the building's structure.
Flat roofed buildings with rubber roofing use a ballast of aggregate to protect the roof from uplift from heavy winds.
The roof cladding must be able to insulate a building's interior from the exterior temperature. Most often, this is accomplished with rigid foam insulation.
However, other methods, including building up multiple plies of roofing and shingles with high thermal mass, such as terra cotta or slate, can insulate a structure from the roof.
The roof is very exposed to the sun and the ultraviolet waves that emanate from it. Roof cladding must be resistant to sun damage.
So, roofing is often not composed of plastics or wood. Instead, durable materials are used to produce roof cladding.
Asphalt, slate and steel are excellent against the sun's rays. The ballast on rubber roofs acts as a sun block, protecting the roof from the degrading solar radiation.
Future Roof Cladding
Although many man-made materials are not appropriate for use as roof cladding, advances are being made with vinyl and other materials to allow them to be used as roofing. In fact, some roofing composed of man-made materials, such as fiberglass, are already being sold.
As technology improves materials and methods of creating roof cladding, we may see other new materials, like ceramic, or we may find roofing is applied in broader sheets, covering more surface area with less labor.