As the foundation to the existing garage is not likely to be traditional it s probably a shallow slab a new foundation may be needed for the new wall.
Garage door infill.
The interior will be less complicated largely requiring just drywall as a cover.
However a single garage door at eight to nine feet wide and seven to eight feet high is a common measurement for many homes.
Our partners at clopay offer custom garage doors in a variety of sizes.
Choosing a garage door size.
If you need a double garage door the typical measurement is 16 ft.
There is no standard garage door size.
Remodeling the garage door area appropriately will make the wall space look original to the house design both inside and out.