We generally call an RV garage home anything with a 12 ft or higher garage door opening. As recreational vehicles are getting larger most Motorhomes or 5th Wheels may need a 14 ft garage door.
In current inventory you can find double RV garages and occasionally even a triple RV garage. We are a town that likes big boy toys. The depth of the garages can be anywhere from 40 ft deep and we have even had 100 ft deep garages.
Once you know how much you want to spend start shopping.