I think in NJ it depends on the "local" codes. When I lived up there, if 100 sq/ft no floor/foundation required and not taxed. If over 100 sq/ft floor required, and taxed. Plus permit required. The county where I live in Florida, now requires a permit for any prebuilt shed/garage, regardless of size. Same for a metal carport. My original metal carport (approx 20x20) is "grandfathered in" with no permit with a dirt floor. If it had a concrete or asphalt floor, it would have needed a permit. Carports and "sheds" need to meet wind codes