My observatory is 9ft 6in x 9ft 6in and I certainly wouldn’t want it any smaller. If I was building again I’d make it 10ft x 10ft. But then I’m a visual observer who needs to walk around the telescope and climb up step ladders etc. I’m pleased I made it very substantial. It is bolted to the base by studs cast into the concrete – essential when you live close to the windy east coast. It also has a damp proof membrane to protect the wood
British Astronomical Association
Supporting amateur astronomers since 1890