[stellar2]

Trying to keep costs down, I used as my original observatory a commercial shed about three metres square made of zincalume. First, of course, I had to sink a pier for the heavy mounting I planned to buy. That was straightforward; a large hole, a length of concrete pipe, a quantity of reinforcing steel, and a load of cement. I assembled the shed around it, resting on short piles made of treated pine. This was in my grassy back yard.
I rebuilt its roof as a roll-off, with large rubber-tyred wheels running in extruded aluminium track fixed to timbers. This structure worked well, but was uncomfortable in the Canberra winter, as the temperature inside went severl degrees below the outside (already freezing!) temperature on clear nights. I decided on a fibreglass dome which, with its amaller observing opening, would be less frigid to work in. I'd worked in domes at Mount Stromlo for fifteen years.
The dome was lifted on to a new, flat roof with a circular aperture, and always worked well. It was certainly less windy and cold inside!
But there were two things wrong. The piles on which the shed's frame rested were too close to the grass. And the flat part of the roof was never able to keep out rain. It always leaked at the joints, no matter what I tried to seal them with.
As a result, water got into the floor supports and also the particle board flooring I had fitted (with carpet on top) and before I knew it the floor and the joists collapsed as their timber had begun to rot. I don't have either the energy or the funds to rebuild, but I have to say, avoid flat roofing as it is not possible to make it waterproof! A dome needs to be on a circular wall. A plastic water tank might be good. Floors need to be at least 20 cm above the ground.