Lightweight and resistant to fire, metal roofs can be made from aluminum, galvanized steel, copper, zinc, stainless steel, and titanium (the most expensive).
Metal is more expensive than asphalt shingles, but are longer lasting and require less maintenance. If installed properly, the only threat to a metal roof is rust. However, rust can be controlled with the application of protective paint, rather than replacing the whole roof.
Metal roofs are ideal for warmer climates, such as the southern United States. As metal reflects heat, cooling costs will be reduced dramatically with proper insulation.
Metal gutters and downspouts attached to a metal roof can be more aesthetically pleasing, as there is continuity in their appearance. However, it is necessary that sealant is applied at the gutters to keep it waterproof.