the two by fours are just regular ones, so is the ply for that matter.
i am assuming you are talking about our circular trough construction- i like 3/4 ply for the flat sections like the lid. we recently tried some half inch, and it just doesn't hold as well, it wants to warp too much, it is too thin and floppy.
creating the outside curve was quite the experience. we used a very thin plywood for that, and even then the wrap was difficult. with a 5 ft circular, it would be even tighter, perhaps impossible.
i would consider using FRP for the wrap, maybe twice around for extra stability, with the seams staggered. i would still use the 2x4 posts on the inside as vertical supports. the 2x4s are notched 6 inches or so, so that the notched out part sits on the top edge of the trough, and the extending notch sits inside the trough. kinda hard to explain...
you would screw in through the FRP, into the 2x4s, from the outside, as you worked around your wrap. i would worry about the screw heads popping through the FRP, so i would use a strip of wood, like 1/4" thick, providing a base for the screw heads at each 2x4 location, on the outside of the FRP, you dig?
wrapping the outside around was made possible by using our metal bander. we ran two 1/2" metal bands around the whole thing and tightened it up snug before fully securing it with screws. you could do that same thing with straps, but we had a get some pretty good torque on it, so i don't think hand tied rope would work, you need some leverage.
the lid was just a top cap, it wasn't attached to the walls at all, but it was quite heavy, as it was framed with on end 2x4s, so 5 inches thick, and it sat secure under its own weight. we added a couple of 4x4 posts across the middle of the cage, supporting the lid from underneath, because the 10 ft gap was so wide. for a 5 ft cage, i would go with perhaps one center post support.
those are the details off the top of my head : )
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robyn@proexotics.com
Pro Exotics Reptiles
