At a certain width, things become prohibitively expensive or you need to start putting up center posts.
For that many you will need a LARGE garage, but I would suggest making it a long building with a number of bays to pull in/out. say 30 X 120 or 40 X 150.
This also sets you up nicely for future expansion. If you need more space later, it's no big deal to add more "frames" onto either end of the structure. However if you anticipate growth, place the original footprint accordingly.
Oh, and like they all said, build it at least 2-3 times bigger than you think you will need. If a normal vehicle takes a bay to house, a disassembled/project vehicle will take 3 while you are working on it.