We have 2 metal Garadors. To make them look like wood, we used Dulux Brushwood. This is a 2 coat system - the base coat is reddish brown, and the top coat is darker, but semi-see thru. This adds the 'grain' over the first coat. I'd recommend it, but with one important reservation - don't use their first coat (which is/was WATER based) on metal or plastic, as it can peel - use a normal ('oil-based') paint of the same colour instead.
When our second metal door was delivered to finish off the new second garage, the driver said "Why did you buy a metal door? That WOODEN one you already have looks a lot better" 'Nuff said...!