I ran into a few problems during the build and the strength of the rings was probably the biggest headache. Even though I used 3 laminated layers of 12mm plywood in the dome ring, it would still flex. This eventually caused the dome to crack open at one stage which upset the shutter track. Same can be said for the wall ring. It flexed out of level as more weight was applied. It would be wise to fit wheels as close to a wall support as possible to avoid flex in the wall ring. I would also suggest steering away from wheels and using a track as part of the design. A bent pipe and wheels to suit would be ideal.