Specialty garages are considered specailty when they have a certain design to them. This design usually comes in 2 ways.
The first way is a garage with a lean-to on either side. A lean-to is a separate non-enclosed addition to the garage for extra storage. This is when you have a 20x21 garage then you add a 12x21 lean-to on either side giving you a 32x21 structure.
The second way is a structure with only a certain portion enclosed. We consider these to be a garage with a porch. This is when you have a 20x41 structure but you only enclose 20x20 of it leaving 20x21 open on either end.