I'd like to have a garage big enough to park the 747! It would only have to be about five feet longer than our current one, and maybe 10 feet wider, if we were also going to park the truck. But that would put it in our nextdoor neighbors' living room!
Are you still thinking about relocating?
No sense building a garage and then moving.
On the other hand, if you could accommodate at least one vehicle, then you could service them, or whatever, one at a time.
It would probably be fairly easy to make the garage five feet longer, perhaps incorporating a balcony to the floor above. Might even be worth it for the resale value.
Use the existing door header as a ceiling beam, and "slide" an expansion out toward the driveway.