Hello,
Try something like the link below. If nothing else it will take you through each step and tell you different ways of doing each step. Then its up to the resources and DYI abilities available for what might be a workable design.
I did think about a roll away shed option last year, found that the district railway society had a good price on the old railway rails. Great bit of infrastructure for next too nothing for the price of steel. Think I was quoted $120 for a length. Like the idea of the shed roll away over the roof, seemed like it would be easier to do.
Steve
Ps. Obs sheds do turn up a few times a year, 2nd hand here on the classifieds.
Designing & Building a Domed Astronomical Observatory
David Greenwood & Chris Lord
https://brayebrookobservatory.org/Br...omed%20Obs.pdf