Classed as temporary structures, sheds and wooden outbuildings rarely require planning permission, unless you live in a conservation area. They can be built almost anywhere, so long as they are positioned on a level, firm surface. You'll find lots more advice and ideas on garden buildings in the book Outdoor Living: the Inspirational New Step-by-Step Guide to Today's Outdoor Living Space from B&Q. Greenhouses come in many shapes and sizes, with frames in timber or, more often, aluminium, which has the advantage of being maintenance-free.