YardPods feels like a much more American term for a place to shedwork than a garden office and so maybe Northern California YardPods is onto an industry winner with their prefab, steel framed buildings designed for your back yard/garden (see here for why they think steel is better than wood). You can get kits to do it yourself or get them to build the whole thing. There are some nice touches - LEED Certified recycled cotton fibre insulation, formaldehyde-free plywood, and a range of roof styles. All YardPods are designed and built to order.
Via most of the interweb but first seen at Tiny House Blog