How small a shedworking space does one need? The Thought Box from Holly Palmer is probably as small as it gets. Apparently it "promotes mental efficiency" in the user and has been built to fit beneath your chair when not in use. Here's what they say about it:
"It is intended as a personal space in which to simply think, using sensory deprivation to exclude the outside world (ear plugs improve this further). This allows you to reach total relaxation as your mind doesn't have to process other signals."