Larger lizards pose larger problems when it comes to housing. Any custom enclosure is going to present custom problems in usable space, uvb/ir lighting, heating, humidity and cleaning. If this is an indoor enclosure it may require custom dimensions, and outdoor may be battling the weather, and one that can be moved from one to the other can severely limit the overalls size, weight, and water features.

Iguanas:

Young iguanas can be housed alone in some of the larger off the shelf 40-50 gallon enclosures or a 100 gallon melamine. But as an iguana reaches maturity they require much more space. At bare minimum, an adult will need 10ft by 5ft of floor space and at least 6ft of height to climb. 

The following enclosure is both indoor and outdoor connected by a passage way. Having an ability to block that passage and lock the iguana on the other side can make feeding, cleaning, and servicing much easier and safer. The is especially true when dealing with a pond and filter system.  There is ample climbing room that is not too steep and lots of places to bask. Large uvb lights and halogen basking lights would be positioned above the basking spots and protected by wire mesh to ensure the iguana cannot touch them. While the bark and logs are visually pleasing, if not sealed properly they my become difficult to clean. Also note how the water feature is raised up allowing the filter plumbing to be hidden blow. This also allows easier draining when you need to service the system.

Consider the following enclosure and how adding a raised pool at het bottom with a hidden filter system would make all the difference in how this enclosure both looks and functions. In this case the loss of real estate at the bottom to gain a large pool would be worth it. This would complicate feeding though, again, custom enclosures all come with custom problems to solve.

Lighting:

Recessed lighting is one of the safest ways to implement your fixtures as it is easy to screen to protect your inquisitive lizard. This also works for bar lights , you just need to cut a rectangular hole to match.  Make sure to engineer a way to easily get at your lights for bulb replacement. Also consider an extra amount of distance from the screen for high output lights like mercury vapor or Halogen lights so the wire doesn't get too hot.  Large enclosures require larger more powerful lights. I have found that large deep dome dimmable fixtures with build in rheostats (dimmer switches) are a low cost but highly effective way to implement halogen lights instead of your typical incandescent spot bulbs. The halogens can produce the same heat for half the power consumption and the dimmer switch allows you to control the resulting temp at the basking spot. Be careful to select a flood style halogen or spot bulb, some of the reflectors on non flood style beams can create intense hot spots at a distance like a magnifying glass which can burn your lizards skin.  Make sure to read up on UVB lighting for lizards on our site to understand the basics of distance and power of light before you commit to buying something as they are not cheap!

Below is a great example of a protected l;ight box with recessed lighting added to the inside of a custom enclosure.

This runs both a UVB light and Halogen light for daytime heat

Make sure to protect anything that is hot or can electrocute your lizard with the appropriate type of cage if your light or heater is not recessed. Industrial cages used to protect fire alarms at schools make good cages capable of holding up to the strength of a large reptile. The small cages often found at reptiles stores will not hold up to a large lizard at all.

Basking area:

One of the smartest ways to implement a basking area for a big lizard is to place a thermostatically controlled heat mat under dark slate tile. It is best to use a Flukers style heat mat and recess all parts including the cable and temp sensor into the shelf below so the tile can sit flat. I used a small inexpensive harbor freight hand held router to make quick work for the example below. It is important to place this shelf under the basking lights so your lizard is compelled to bask there. The heat mat thermostat is set to a moderate temperature which is mostly to add overnight heat, the basking lights will help heat up the slate tiles during the day so choosing a dark tile color is best to absorb light. Finally, and the big bonus, your large lizards nails will all be filed down nicely by frequenting the tile so handling doesn't have to include scratches anymore. Making this basking spot font and center of the viewing area of your enclosure also encourages your lizard to present themselves out in the open where they are most majestic.

Big lizards just love lounging on heated tiles, and its fantastic at keep sharp claws in check.

Water Features and Ponds

A note about water features and ponds. Lowes has some great pre formed pond liners that are inexpensive and easy to implement in a custom enclosure. Many are pre plumbed with bulkheads to allow easier implementation of a filter system.  There are lots of sizes to chose from to and many can work together like the two below to make a small water fall. This is not only aesthetically pleasing but can dramatically increase the environmental humidity levels to what many tropical reptiles need. 

There are two products that I highly recommend for waterproofing a custom enclosure, both called Drylok. The original is mixed with sand so it dries with an abrasive surface, the extreme goes on smooth with a surface that is much easier to clean. The can both be found in white or gray. There are uses for both, choose wisely. Both will take concrete color so you can get pretty creative with it. All of this should be readily available at your local Home Depot or Lowes. Tip: Ultra smooth surface should be roughed up a little bit with 60 grit sand paper. Make your fist coat very thin and wait for it to dry before applying the second coat. This acts like a self etching primer. The second coat can go on very thick and the final result will be very durable.

Pumps and filters:

 A large lizard is going the need a large pump. If your enclosure doesn't have a lot of loose substrate that can be pulled into your water feature, the flowing pumps work pretty good and are easy to service.  This is at the low end of a pump system, you may need to size up much larger depending on your specific situation.

Cleaning

As hinted to before, cleaning should always be a consideration to your design.  Some of the best large lizard enclosures with ponds are designed to be sealed into the floor and collect all the runoff from inside your enclosure, much like a stand up show does.  This is an amazing help to allow you to hose down the enclosure after a deep clean and all the debris flows into the pond. Now drain the pond bypassing the filter and you have easily serviced the whole enclosure including a complete water change.

Putting it all together:

Large custom reptile enclosures take time, planning, and often times a small bit of rework. Sometimes the best laid plans are thwarted by a not so cooperative lizard. Much like a cat that prefers the box the toy came in over the toy, you might find your lizard uses your enclosure differently than you expected.  If you make everything you do as adjustable as possible, you might be able to move this around to accommodate, or they might send you right back to the drawing board. Don't get discouraged, the end result is always going to be better than the alternative of a small off the shelf enclosure!