garden studio ~ this would work just fine!!!
Google Image Result for http://www.michaelsgardenoffices.co.uk/home%2520page%2520photo/DW%2520-%2520final%2520-%2520front%2520page.JPG
Contemporary Garden Studios | Eco Outdoor Studios - Ecospace Studios
Note siding, amount of glass and how it extends into corner.
office in my garden: Office In My Garden
10 x 8 Waltons Contemporary Garden Room Wooden Summer House with Side Shed