Easy to do and it can solve alot of problems.
Making garage door taller.
What kind of load is the header over the garage supporting.
Wall extensions because garage doors are usually sized to snugly fit the dimensions of the garage itself making the door larger usually means making the garage larger.
Have your contractors figure this in.
You are only raising the roof line the studs can be extended by installing say a 6 stud 3 4 of it above the top of the existing stud you will have to remove the top plate and save as you can then re attach it to the new top of the walls double plate included it depends on how your garage was made.
One way to do it would be to get wall extensions for the entire the garage and then cut the roof of the garage off lifting it up to the height you want it.
Usually 4 or 8 feet.
I removed some siding and and re did the trim on the top of the door and then recovered every thing with aluminum and installed new rubber garage door sill around the opening.
That made my door height two inches taller.
That is the side where your truck is to go you can build out on the back side.