John,
PBR metal roofing and wall panels are mostly fabricated from manufacturers' 22, 24, or 26-gauge steel panels. (22 gauge being the heaviest and 26 being the lightest gauge) Though 26 gauge is used on many residential applications, I prefer 24 gauge over solid decking applications. 22 gauge is mainly used over open framing situations but can certainly be used for solid decking. The material is usually galvanized or galvalume and available in multiple colors depending on manufacture.