We've covered shedlike atmospheres with fewer than four walls, garden offices where there are no gardens, shedlike structures which are (almost) invisible, but I can't recall one without an actual roof. Oliver Bishop-Young seems to have cornered the market in bespoking skips for other purposes such as playing, relaxing and gardening. He's not yet set up an office skip, but it surely can't be long before he does. The example pictured is perhaps the nearest he's come so far.
Via An Artist in Beacon, NY