If you are building a cage higher then 3-4ft. I would suggest a good depth of soft substrate because in the wild/captivity frillies will jump to the ground from high places and they can tramatize their digets by jumping down onto a hard surface, I experianced this before. I would put a nice layer of sand/mulch or something to cush the blow to the body if they do decide to jump down like mine use to do quite often.
Bob
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