[Porsche-O-Phile]

As has been said above, you almost certainly will want to buy a door pre-installed in a frame, which naturally you'll be charged extra for - a lot of times almost double the "door only" price. If you're absolutely certain you can get the door to work with your existing frame without having to set and re-set the hinges a million times (mangling the screw holes in the process) then maybe you can save a few bucks and go "door only" but I wouldn't recommend it. Whoever owned my house last obviously tried to go this "cheap" route on a couple of the doors and the frames are butchered beyond belief where the hinges were obviously hung and re-hung several times to get it right so the door would swing freely and not bind. With a metal door/frame this would be even worse. The easiest and simplest way to go is to measure your R.O. and get a door plus frame, pre-hung, to fit that opening, shim it as necessary to make it level and square, attach, install your hardware and call it a day.

If a fire rating is required, you will pay more for a rated door assembly. You also need to consider whether it requires or should have a smoke seal.

Is the garage heated? If not, you probably want a decent-quality, insulated metal or solid wood door. Stay away from hollow core doors (even for interior spaces). Pure crap.