For sectional-type doors mounted on steel jambs, the width of the door is 2" more than the opening width. eg: if you have a 10-0 wide opening, you'll order a 10-2 wide door. Standard (commercial) door widths are 10-2,12-2, and 14-2, and it's always better to stay with standard.
But...since door sections are roll-formed, the length of the panel is only limited by practicality and wind load. I once sold/installed a door that was 56 (fifty-six) feet wide and 2 (two) feet tall.
Door heights are a different matter. Normally, the sections come in 21" and 24" heights, so you can stack-up just about any height you need. There may be other section height options, so take a close look. A door can overlap the opening height, but doing-so can cause issues with outside lock/lift handle hardware and/or head weatherstrip.
If the door is over 12 feet high, I'd suggest you get a
reduced-drive (as opposed to direct-drive) chain hoist and 3-inch track. IMHO, 3-inch track is the difference between a 10-year door life and a 50-year door life.
A standard door comes with 10,000-cycle springs - a cycle being any change in the door's position. Think about how often it will go up and down. It doesn't cost much more to specify a
reasonably higher cycle life. For example, if you spec 100,000 cycle springs, you'll likely get upgraded to pillow block bearings.
One really important thing is to determine how much headroom you'll have. There's no such thing as too much headroom, but not enough is a
real problem. Same goes with sideroom.
If you opt for an electric opener, you have two choices. The drawbar type (sometimes called "trolley") is good and positive and reliable. Downsides: 1) the door can be a pain to disconnect and operate in the event of power failure, and 2) it can destroy the top section.
Your other choice is a jackshaft type opener. A good jackshaft opener will have a floor-accessable disconnect with chain hoist backup operation.
When looking for doors, if the salesman doesn't walk you thru all the above, then he's not the right guy to be talking to. Ask the salesman if he recommends "pusher springs". If he does, don't walk from that dealership - run like Hell!
I don't see a lot of quality difference in the doors I've looked at lately. The key is to get a good installer. Even the highest quality product will self-destruct in short order if it's not installed properly. I don't know you...but with all due respect, if you install the door yourself, it will not be installed properly
Bear in mind that an electric opener is not a remedy for an improper door installation.
And lastly, like so many other things, a door is only as good as the availability of parts and service.
Well...that was long-winded