The roof ribs are fairly stiff on their own after 4 layers are glued and screwed (and allowed to dry)
NOTE : EDIT I used 4 layers as 3 turned out to still be too bendy and springy
Moving section is 2.4m x 2.4m (or 8 x 8 for the traditionalists)
I used standard 8 x 4 exterior ply
One end is braced by 2 x 4 timber and a complete filled plywood arc , this stiffens the roof and discourages it from trying to flatten out.
Depth of the ribs is 75mm (3inch) which seemed to be enough to resist flattening but not lose too much roof clearance.
The ribs were fitted to the moving beams using sections of " 2 x 4 "CLS between the ribs and screwed to the beams and the ribs
Over the ribs I covered it with 7mm wall cladding (89mm wide strips) that tongued and grooved together , these were nailed down to the ribs.
This is the internal skin , I wanted wood as metal surface would create condensation.
Over the cladding is a layer of "Protex" waterproof but breathable membrane.
Outer layer , not yet fitted , will be sheets of galvanised steel 1mm thick , these get screwed down onto the rib positions with rubber washers under the heads to keep water out
heres a photo that shows the basic design