Ok finally worked out how to place low res pics on the forum without it crashing.
I bought some form ply, treated pine and other materials at Masters when they were closing down. up to 70% off the price of the form ply sheets.
The cubby was also not square so i had to make a frame around those TP posts.
Reused the roof poly but made a new light weight roof frame, with a vapour barrier to catch condensation.
I used two angle braces to form a track for the castors. the size is about 2m x 2m so 4 castors would be OK.
Put a couple of blocks at each end so it would not roll of the edge.
I used some cargo straps to tie the roof down when closed and when open I have four elastic straps to keep the roof from blowing away when open.
For weather sealing, i used some plastic flashing which overhangs the walls by 10mm when the roof moves it just flexes over the walls. Same goes for the fascia it has a 10mm overlap with the walls to keep the rain out.
I also put in a couple of vents to each gable to improve air flow.
Put an external powerboard in from the house, which also serves as ethernet over power to get onto the network.
Enough room for a chair and bench.
No was was i gong to try to put in a pier all the way to the ground, so I stiffened up the floor with some steel and a post wedged up hard from underneath. Doesn't bother the rabbits a bit.
Dry as a bone after 40mm of rain yesterday.
The pics speak for themselves. Cheers.