The first thing you need to do when you are preparing to free roam your iguana is read Iguana-Proofing Your Home. This will help you make your iguana's free roaming environment safe. Be sure you don't skip this most important step! Secondly, decide what places of the house you want to let your iguana have access to. Do you want it in the family room and bathroom? In a spare bedroom? Will you allow it to roam your entire house? No matter what area you choose, you have some prep work you should do before you just run in and set up a basking spot.
1. You should spend several days observing the angle of the sun and how it moves. Place thermometers throughout the area and check them several times a day to see how much heat is produced in your home during that season. That way you get an idea of how much extra heat you need to provide. Checking temperatures is something you will need to do quite often once you get set up, because time goes on and seasons change.
2. As you did for temperature, you should check for humidity. Most likely it will be low enough to not make a difference where you are, but you might get lucky and find a place that has higher humidity.
3. Once you have an idea of the temperature and the sunlight your designated spot gets, then you can actually locate the site for the basking spot. A good location for the spot is near windows. Iguanas often like to watch what is going on outside. However, you have to keep in mind that the iguana should never be left near an open window (including one with screen) without direct supervision. Areas near windows also tend to be hotter at different parts of the day, so it would be prudent to measure the temperature changes so you can better provide the right warmth for your iguana.
4. Now, you need to build your basking spot. There are an infinite number of ways to do this. One way is to use an old shelving unit covered with indoor/outdoor carpeting. You can glue Velcro to the unit, as well as to the carpet, and when it needs to be cleaned you can just pull it off and take it outside to be washed. Have a spare piece of carpeting ready so that your iguana doesn't have to wait for a surface it can easily grip and climb on while its carpeting is being cleaned. You can also use inexpensive wood shelves, also covered with indoor/outdoor carpeting. You just need to make sure that the shelves are secured to the wall so they aren't knocked off, followed by a hurtling iguana. Also be sure they can safely support your iguana's weight. You can also use the shelving that is made for closet systems (usually white vinyl coated metal), which is easy to make secure and just needs some of the indoor/outdoor carpeting to be made comfortable. This type of shelving has the advantage of being easy to clean and disinfect, too.
No matter what material you use, it must be easy to clean. It should be long enough for your iguana to completely stretch out, and wide enough for your iguana to turn around on easily. It should also be long enough to allow for a temperature gradient, so your iguana has a cool side and a hot side. If you feed on the basking spot, it needs even more room to accommodate a food plate/bowl and a water bowl on the cool side, and accommodate the full length of the iguana on the warm side. If you so choose, you can have the food and water on another side of the basking area, but you have to make sure that the iguana will make the trip to the warm area to bask and digest.
5. Your iguana is going to need some way to get up to the basking spot that doesn't involve climbing your computer equipment to get there. Just about anything can make good ramps or climbing poles. The previously mentioned closet shelving comes in a variety of lengths, and makes for good ramps or vertical climbs to basking spots (do not cover with carpet for this, as the spacings allow for adequate clinging with toes while doing a short climb). You could use a 4" PVC pipe covered in indoor/outdoor carpeting that has been bolted to a flat base, then bolted to the basking spot, to encourage climbing that resembles climbing an upright tree. Also, wooden beams work for the same thing. They should also be covered with indoor/outdoor carpeting so that a grip can be established. You can also use a natural branch (disinfected, of course), and any choice you make can be placed directly vertical, or at an angle. You could use milk crates tied together as a "ladder" to reach the basking spot, or an old chair that you don't care about can be used. Use your imagination, and go with what makes you and your iguana happy.
6. Now that your iguana can get to the basking spot, you need to make your final decisions about light and heat. Of course, UVB bulbs are mandatory, unless you live in an area where you iguana will get basking time in unfiltered sunlight almost every day. Be sure that you position UVB bulbs so that they are no more than 15" away from your iguana, because the UV light will not travel any further than that. For heat, a spotlight works well for the hot side of a basking spot during the day. You can also use a CHE, but many iguanas like the psychological factors of having a light on them that heats them up. You may have to use supplemental lighting in the free roaming area to make sure the heat gradient is sufficient. Be sure to position all lights in ways that will not allow your iguana to climb or jump on them.
One of the hardest things to control are the temperatures that are on a diurnal cycle. For instance, it can get horribly hot in the afternoon in the room of an iguana who has western facing windows, so the light that is for heating needs to be tailored to avoid overheating the iguana. This is why it is so important to do the initial temperature recording, and to recheck the temperatures after you put the lights in before the iguana is put into that situation.
Allowing your iguana to be a free roamer in your home can be an excellent way to be sure it gets adequate space. However, like everything else with iguana care (or pet care in general), preparation and planning ahead are essential for success. Be sure to keep safety factors in mind as you set up your iguana's free roam area, and of course, be sure that the environment you provide will meet all of your iguana's needs. Be creative, test things out, be willing to make necessary adjustments, and let your iguana tell you what works and what doesn't. In no time, your iguana will be happily, safely, and successfully free roaming.