Just my 2 cents worth: a previous poster said not to use cedar, but I’m not exactly sure why. I’ve read several anecdotes warning that the resins present in most conifer woods can be slightly irritating, but I’m not sure why cedar is off limits. I have no idea of the kind of lumber available in your locale, but the cedar sold around here is the wood of various thuja species, and not actual cedar, which is in the genus Cedrus. The most common types of dimensional lumber sold for construction purposes in my locale are spruce, pine, and cedar (thuja, not cedrus). All are conifers and all have resin that can cause slight irritation. For outdoors, the two types of lumber commonly sold are pressure treated spruce or pine, and untreated cedar. The former are treated with an arsenic/copper compound as a preservative against the elements, the latter is untreated and contains only what nature has givrn it. Between the two, use cedar all the way. Your next option would be to use dimensional lumber for finer wood working. Your options range from poplar, birch, oak, maple and pretty much any other commercially logged wood that your willing to pay for. All of these latter types of wood will need some kind of water repellent to avoid mould, fungus and rot. Various safe types of repellent include linseed oil, vegetable oil and the like.
Sorry, I’m totally not trying to snow you with options here...the long and the short of it is thus: don’t use pressure treated lumber if you can help it. Resinous conifers might pose some kind of risk, and cabinet making timbers are no guarantee of safety: oak, for instance, is toxic under certain conditions. In reality, however, you’re looking at less than 10% of your enclosure’s total surface area, and furthermore, chameleons are often in contact with toxic woods in the wild. Even stronger, if you screen your enclosure on the inside of the wooden frame, offset if you want to be super careful, the likelihood of toxic reactions is...well...probably not something to worry about. My sole caveat is with PT wood. Heavy metals such as copper and arsenic are probably the kind of thing to avoid if possible.