Assuming the metal is bare steel, it is not subject to traffic, it is clean, dry, sound and prepared as detailed in the technical data sheet we can recommend Rust-Oleum 3369/3380 CombiPrimer Anti-Corrosion followed by 2coats of Rust-Oleum CombiColor Original.

This is available in many RAL, NCS or BS colours in a satin or gloss finish.