Sounds like you're looking to build a greenhouse of sorts, very cool idea! I'd build it well away from any trees, I suspect it would not hold up well to a large limb falling on it! You might also consider some underground retreats in case, for whatever reason, the fans shut off in the summer. I only have experience building more standard outdoor housing but here are a couple pics to better illustrate the underground hide. It's a nice, cool retreat in summer and doesn't get freezing in winter.
This enclosure was built for a tegu. The underground hide is buried below the frostline under that bare patch on the right side, outside the enclosure.
The tubing under the chair leads down and into a large box that's buried under that patch of dirt I mentioned in the above picture. The chair helps keep water out when we get windy rains.
Living outdoors your animal will definitely be alot dirtier most of the time. It was far and in-between that I got a picture of my tegu when he wasn't all brown from digging around - this is not one of those pictures!
Heading to bed for the evening..
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