like you said Plexi can scratch... and it WILL SCRATCH... Also if it's not thick enough it'll CRACK... plexi wares with ages, so you may want to place it some where in which you can easily replace it if it becomes undesirable .
I'd suggest a wood and plexi combination using the plexi as a door/window
be sure to coat the wood with polyurethane to make it water proof and you can go a step further and place vinyl tile on the cage floor...
also you will want to seal the inner groves of the cage with silicone so that moisture doesn't seep in and expand the wood.
how you choose to construct a door/window can vary greatly I think that depends on various factors such as the size of the cage, how you would like to gain access to inside of the cage, where the cage will be set up and how readily accessible the door/window will be when/where you do set it up.
Hope that helped




~ZF
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Royal ReptileZ