Roofing is layers of various impermeable material nailed and glued to a wooden deck the combination keeps home dry. Using quality materials pays off for the long run and skimping could be costly.
As my picture shows a “professional” roofer nailing asphalt shingles placed over tar paper stapled to the wooden deck. He is careful to line up the individual shingles ensuring that even spacing and maintaining alignment.
Roofing shingles vary in quality and their life warranty by their manufacture normally they last anywhere from ten to twenty odd years before needing replacement. Nature and area where the home is migitates in shingle life.
This is my contribution for WP single word prompt:”LAYERS”.