Hi guys,
Here is a link to a web site I did for my iguanas a really long time ago:
http://www.geocities.com/heartland/5844/cujoang.htm
If you scroll way to the bottom, you'll see a cage I built for Cujo when he was young. I used branches found outside that I tried to sterilize by letting them soak in a swimming pool (it was end of season and since we were getting ready to shut it down for the winter, I tried to use make a sterilizing bath out of it by adding a ton of chlorine to the water). I then rinsed them thoroughly and let them dry in the sun.
This didn't work, though, because I ended up finding little bugs in Cujo's terrarium (naturally, once the branches were all installed in his terrarium). It wasn't a MAJOR deal in this case, because I only found one or two ants and a few little flies which died after a couple of weeks, then the branches were okay. But this is just something to keep in mind. Large branches are very hard to sterilize. You need to be able to *completely* submerge them in a sterilizing solution (bleach) or bake them in a 250F oven for several hours.
The configuration of the cage, though, works really well. You want to provide plenty of climbing areas and plenty of resting areas as well. Igs can't rest comfortably on branches that are set at too much of an angle. You also want to set up a basking ledge, i.e. about 12" below a full-spectrum fluorescent bulb and with a basking light pointed at the ledge. If you look at the middle ledge, you will see that there is a food dish there. I cut out a hole in the ledge so that the bowl sinks, so it doesn't get knocked over and makes it easier for the ig to eat. it's also more natural for the ig because he doesn't have to go down to the ground to eat.
Anyway, I hope this gives you some ideas! There are a lot of thing to consider when setting up a home for an iguana. For example, this terrarium worked well for about 2 years, but as Cujo got big, he eventually destroyed all the plastic plants and made a mess of his walls and floor. For large igs, it's really better to sacrifice beauty for practicality. Wire shelving works equally well, too. 
Julie