The first thing I did was adjust the front facade of the building to match the prototype photo I have showing how the large overhead doors were arranged before they were boarded up at some point in the 1990s. (See this photo)
This required cutting one new opening in the front wall and enlarging the opening with the two smaller doors. As I was enlarging the door openings, I made sure to allow enough space for the two windows above each smaller door.
Before I cut the openings, I tried to find commercial garage door castings that would work. Everything I found in my stash of gas station kits and plastic doors were either too short, too wide, not tall enough, or too tall. Scratchbuilding was the only option.
I tried two approaches to the garage doors. For the taller single door, I started with a piece of Evergreen .015 clear styrene, cutting it slightly larger than the opening to provide a surface to attach it to the door opening from the inside. Then I added styrene strip for the vertical and horizontal portions of the door. A coat of white paint - being sure not to get any paint on the window "glass" completed that door.
For the two smaller doors I cut a rectangle of .015 styrene wide enough to accommodate both doors and the center post between them.
Then I cemented the trim strips to the styrene base. The vertical trim was fairly straightforward, the horizontal trim pieces were installed overlength and then trimmed to fit with a fresh razor blade.
One everything dried, I carefully cut out the door openings and filed them square. After painting, I'll add clear glazing to the windows.
I can't say I like either of these approaches better than the other - if you needed a door painted a color other than white, I suspect the second approach might be a little easier.
One thing I do know - it was far easier to scratchbuild these than the two or three evenings I wasted trying to find a ready-made solution.