12′ x 20′ Custom Built Storage Shed with “Garage” (CU-5) By Mary Steele on August 1, 2013 in Custom Built Sheds, Portable Building Styles We built a 12′ x 20′ Ranch style portable storage building and modified it to include a set-back garage for the owner’s riding lawn mower. Model CU-5. Construction Features Customization Options Rent to Own