The gauge for a metal is the thickness of the metal being installed to the roof. The higher the number the thinner the metal panel. For a real-life comparison, an aluminum can of soda is typically a 37 gauge metal, whereas the hood of your car is 20 gauge metal. Typical roof panels vary between 22-29 gauges in thickness. With a lower gauge of metal, the cost will increase but so will the durability and resistance to damage. In areas that can have more extreme weather, such as hurricanes, a thicker panel is less likely to be damaged. These panels are usually made of steel, with the exception of homes located near salt water. In those cases, aluminum is used to prevent further damage from the salt water. The striations that are rolled into the panels actually increase the durability of the panels as well. It is not just decorative but provides more support to the roofing system.