Permanent Outdoor Enclosures? - People who live in warmer areas may consider building their iguana's enclosure outdoors. The Green Iguana Society does not recommend this for several reasons.
First of all, an iguana left outside in the heat of the day unsupervised is susceptible to heat stroke. Many people are surprised to hear that iguanas can overheat, because they come from the warm, tropical areas. However, one must remember that in the tropical forest, an iguana can get out of the direct sun at any time to cool down throughout the day. In a cage, an iguana can only go where the cage walls allow. It doesn't take very long in the mid-day heat before an iguana's body temperature rises to a dangerous degree.
Secondly, it is very hard for an owner to properly regulate the temperatures in an outdoor enclosure. Not only is there the danger of the iguana overheating, but there is the equally harmful possibility of the enclosure being too cold, especially at night or during bad weather. Running power cords across the yard to run lights and heaters can be a problem.
Thirdly, outdoor enclosures can be very dangerous. Many animals will break into such an enclosure and attack, injure and even kill your pet. Racoons and opossums are notoriously clever and determined. Roaming cats and dogs are also problems. Even if you think the enclosure is safe, chances are that it is not. Iguanas kept outside are susceptible to the stress that comes from seeing potential predators but not being able to escape. Not only can other animals (and people) get into the enclosure, but your iguana may be able to get out. Smaller iguanas are able to squeeze through tiny openings - gaps in frames and doors, rips in screens, openings in wire mesh. If your iguana escapes outside, it will be very difficult to find before it gets hurt or permanently lost.
Fourthly, keeping an iguana outside means less contact time between it and its owner. Iguanas need contact with their owner every day to retain a comfortable relationship. Owners need to spend quality time with their iguanas to spot any health and/or behavioral problems. An iguana kept outside is likely to become untrusting and difficult to handle.
What about sunning enclosures? - As stated earlier, the best way to provide your iguana with the UV light that is so necessary to its health and well-being is to take it outside for periods of time to allow it to bask in the real sun. One of the best ways to do this is to build or purchase an enclosure that can be placed outside for this purpose. However, there are some important points that one must consider before doing this.
Size-wise, an outdoor sunning enclosure can be much smaller than the iguana's inside, permanent enclosure. However, making it large enough to be comfortable and to provide a range of movement and climbing is necessary. As with inside enclosures, the materials used may vary, but the issues of strength and security still apply. Another additional concern is finding materials that are weather resistant and heavy enough not to tip or blow away.
This is an example of a simple sunning cage. The dimensions are 5.5'Hx3'Wx3'L. It has wheels, and was designed to be moved from inside to outside, and thus was sized to fit through doorways. If you intend to keep the cage outside or in the garage or an outside shed with a larger door, you can increase the size. The materials used in this enclosure include 2x2s for the frame, plywood for two sides, and hardware cloth for the remaining side, door and ceiling. The basking shelves in this enclosure are made of carpet-covered 2x4s, but wider shelves are certainly better. The floor is lined with vinyl flooring, which makes it easy to clean. The plywood sides allow the cage to be positioned in such a way that part of the enclosure is in the shade. A simple cage such as this one can allow your iguana to enjoy the benefits of real sunlight and fresh air while safely enclosed in a comfortable environment.
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. Above all, the iguana should not be left outside unsupervised! 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. In addition, outdoor cages should be routinely inspected for damage, and repairs made when necessary, to be sure that your iguana cannot escape, and that no predators can get in. A properly designed, built and used outdoor cage will keep your iguana safe, secure and comfortable, and will provide it with hours of outside basking enjoyment.
Knock-Down PVC Cage for Iguanas By Catherine Rigby-Burdette is a fantastic page with detailed instructions on how to build an inexpensive, portable, and very functional outdoor sunning cage.