When I bought my house due to having no basement I knew eventually I wanted to build a detached garage in addition to the existing 2 car garage i Have with the house. In the end I will have 576 square feet downstairs, with the attic trusses 14x20 feet of usable space plus another 50 square feet on the landing, so 300 sq foot upstairs, so totaling approximately 900 square feet of space. I actually wanted to take out some trees at rear of my property and go 26 or 28 wide but would not have been within the setback limits. Unfortunately the county requires 15 feet on the sides and 20 feet off rear for buildings more than 600 sq feet. I get away with 5 ft on side and 5 ft on rear for under 600 sq feet of Lower level spacing, which I have no problem doing.