Assuming the garage door is previously painted metal, it is clean, dry, sound and prepared as detailed in the technical data sheet we can recommend Rust-Oleum CombiColor Original.

If there are any areas of bare steel they should be primed first with Rust-Oleum 3369/3380 CombiPrimer Anti-Corrosion or for galvanised steel or aluminium Rust-Oleum 3202 Galvinoleum Primer.