So you are looking to build a mini office in your backyard? This Pre-fab Modular Backyard Office / Studio is well worth a look. It has a modular design and measures 37 x 6.9 x 8.2 ft. It covers an area of 250 sqft. You can combine a bunch of these to create a bigger space.
This backyard studio is waterproof, windproof, and moldproof. It is thermally insulated and has a panoramic window for natural cooling. The full version comes with plumbing, bathroom, tiles, kitchenette, cupboards, and other convenient features.