The thing that is imperative with sunning cages is that they are placed in such a way so that at least part of the cage is not in the direct sun. As stated above, iguanas can overheat very quickly. If you see your iguana panting or gaping its mouth open, it is overheating. Iguanas do this as a last resort to try to cool off. You must provide your iguana with a cooler, shady spot to allow it to cool off if necessary.
Some people even hook up misting systems or a dripping hose to provide a cooling mist.
Providing a pan of cool water for the iguana to soak in to cool off is another possibility. There is too much potential danger, both from overheating and from yard predators. Building or buying an outdoor sunning cage can be a great way to provide your iguana with real sun. It is important, however, that outdoor cages be used with caution and common sense. Iguanas must be closely supervised while in their outdoor cages.