My observatory is pretty much done now so I thought I'd post some pictures of it.
It's an 8'x12' oak post and beam stucture with a roll off roof. There is a small heated computer room and the viewing area has two piers for scopes.
I made it in such a way that should I ever want to move it, except for the roof, the whole structure can be disassembled into the individual oak members and a bunch of 4'x8' panels that can be reassembled some where else.
I built a passive ventilation system that draws cool air from underneath and exhausts it through a functional cupola on the roof.
It's extremely weather tight; I've never had a drop of rain inside.
The ability to walk out of the house and be observing/imaging five minutes later makes life so much easier and pleasant.
For you woodworkers out there, I used half lapped dovetails on some of the knee braces: