One of the simplest most cost effective cages I have see of late are built by Mark one our members, utilizing PVC and fabrics. They are functional and collapsable so they can be packed up and moved.

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Merlin,
What's Life Without A Little Magic!

These maintain heat and humidity great without the problems of having NO air flow like in glass and plastic cages. I designed them initially when living in northern Michigan, doesn't get a whole lot colder than that. There is very little in the way of typical building products for ig cages that insulate the cage primarily what they do is stop drafts and the rapid heat loss associated with them. Think about how many herps are kept in glass which is a horrible thermal insulator.

There is a link in my sig to a bunch of photos of cages I have built (I left the front off many photos for glare reasons from the flash but the fronts zip open).

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~ Mark

Iguanas need a lot of room, and Mark's design is, by far, the most cost-effective way to provide for their needs and provide enough space for them to stretch. They're also the most portable and efficient PVC-based enclosures I've ever seen.

If you want to see what happens when an iguana lover goes mad, here's my iguana enclosure.

I had a similar problem.

Just take into account that it needs to be really, really big, while holding heat and humidity.

But it also needs adequate ventilation. Even the most hot humid sticky jungle has air flow. Without good air exchange your enclosure will get really nasty inside!

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Merlin,
What's Life Without A Little Magic!

You don't need that much ventilation. Anything that slows down the entrance and exit of heat and humidity is a good material for walls. Glass is a very poor material, screen is a poor material, etc. Wood, acrylic, assorted plastics, fabric (check out Mark's cages), and similar are better. You should only use screen outdoors.