2 very common types are Galvalume 5V and Galvalume Standing Seam
5V earns its name from having 5 V's on each panel. These panels are fastened down to the roof deck with stainless steel fasteners that are equipped with rubber washers to create a water tight seal. This roofing system offers a longer life duration than a typical asphalt shingle roof, while also adding that sometimes modern or futuristic look.
The other common type of metal roof is known as a standing seam metal roofing system. These type of panels actually interlock panel to panel. No screws, rather an interlocking system. They are secured at the top (under the ridge cap) and at the bottom (tucked under lip of drip edge). Many believe this look is more aesthetic and less likely to leak because there are no screws used in the securing process.
Either way, metal is becoming much more popular and viewed as the new age roofing system!