Metal roofing has a longer life span and holds up better against wind than asphalt tile shingles. It is lightweight and can be made of steel, zinc alloy, copper or aluminum. If you use copper it will start off with a brilliant reflection and turn green over time (which actually looks really cool on the right commercial building). Steel roofing commonly comes with a painted finish or a zinc coating that helps it last years longer than it would on its own.
Metal roofing normally comes in sheets but can also be formed to look like tiles or other roofing types. Metal roofing used to just be used on barns and outdoor buildings or as an inexpensive material (thin tin) for homes but most people did not like the option because hard rain is very loud on metal roofs.
With better technology out now and better material the sound issue has been reduced a lot and you will see more and more metal roofs on both residential and commercial buildings. After all, the lifespan of a metal roof is around 40 to 70 years. Compare that to a 20 year shingle and it makes sense.