In Ontario, you can generally build a storage shed up to 15 square metres (161.5 square feet) without a building permit, provided it is a single-storey structure with no plumbing, used solely for storage, and accessory to a principal dwelling. However, you must still comply with your local municipal zoning bylaws for setbacks, size, and placement. A 12×12 shed at 144 sq ft falls under that threshold but only if it’s used for storage only and meets all other conditions.