COPPER : Copper generally comes in 16 ounce [standard] and 20 ounce. The 20 ounce generally has more strength and thickness then most roofs would need. Flashings in most cases can be made with 16 ounce copper although with some larger gutters, 20 ounce might be preferred. The advantage of copper is that very few elements will affect this roofing material. Copper is a product that will last a lifetime. Copper roofs can still be found on buildings build over 300 years ago. The natural patina process where the roof will first turn a dark brown and then slowly start turning a patina green. This is a product that actually increases in value as it ages. Copper generally runs about twice the cost of galvanized steel.