I wouldn't call it an observatory, I would call it a place to hide a scope. An observatory is a building to keep the wind and elements away from your telescope whilst it is in use. The shed only covers it. Still roll off sheds are quite popular for large Dobs, I know the ASSA (Astronomical Society of South Australia) have one for their 15" scope up at Stockport. I think they had another one down south too. Good idea but I wouldn't put it up on a platform like they did. Just too much of a risk.