Okay and here is idea 2, this is a great idea if you only want 1 Chameleon
Get a TV hucth. Make sure the depth is at least like 17+ inches, and the width like 30+. Try to aim for the large top hucth area to be 45+ or you may need to drop the floor there. (I will give you some tips if it isn't and you cant).
Seal the wood inside with marine grade epoxy (I wouldnt! use miniwax for this, if it lets any water in, the whole foundation could crumble) Seal all the corners with silicone, (Also I forgot in the last use GE door and windows 1, (no mold inhibitor, 100% silicon). 3 more coats of Epoxy.
Now for the floor you have a few choices, largely depending on the shelf height. If you have 45in plus and want to go the easy way, use pond liner and make a slight steep to the center, you could do this with drywall mud or something (If you go that route, do that before resin and resin the mud in). then put a screened drain in the center. covewr the bottom and a small lip of the sides with pond liner, under the drain.
Option 2, if you dont have 45, but 38ish to 45. Then I would cut holes for permanent pots (dont use the cheap pots that came with cage, buy some nice ones large enough for the plant for always). Recess those pots into the cage, so cut a hole where they will be held up by the lip. Epoxy the inside and build or find a pan that covers the inside cupboards area. Drill small holes in the plants lip so excess water can funnel into the pot, then through the pot into the tub below.
With the plants like this it will give the appearance of a taller enclosure to the cham, as they dont usually go that low down anyway.
Benefit here is A. you dont have to build it, B. It will look like furniture (because it is). Downside, A.This way will be very very heavy, B. if you ever get more chams, it will be very hard to macth depending where you get the entertainment center, hutch ect.
You dont have to spring for brand new, just go to a thrift store/craigslist. You may have to put a more solid back on. Just make sure you clean it will and epoxy it well.
Another option to this Epoxyless. You could take PVC sheet, or Plexiglass, and line the inside with it. Then seam the corners with silicon calking. that should make a waterproof inside, but semi risky again if the silicon comes of and the mdf gets wet you got problems.