In reality, a metal roof can save you money on your cooling costs because it has a higher heat reflectivity than other roofing products such as asphalt/fiberglass shingles, wood, tile, etc. During the summer, it makes the building cooler by efficiently reflecting away sunlight and reducing the amount of heat transmitted into the building.
In the same way, it makes buildings warmer during winter by reflecting inside heat from the underside of the roof back into the building. This good thermal reflectivity translates into energy savings by reducing cooling costs in the summer and heating costs in the winter.