Bluntly, if you have to ask here, you SHOULD NOT have an iguana.
They are not reptiles for beginners. Far, far from it.
Iguanas have very specialized feeding and housing requirements. They can't live on lettuce any more than you can, and what they DO need to eat will take a significant amount of time and effort on your part to obtain and prepare properly. They require regular vet checkups, including blood tests for proper calcium/phosphorus balance. They grow huge -- as in up to six feet long. Yes, a lot of that is tail, but you're still talking about a lizard that is going to need a room of its own. Males often become insanely vicious during their mating season, when they think everything they see is a rival male. Females can become eggbound and need surgery or they will die. An iguana bite can be serious; I had one that decided one day to check out whether one of my fingers was edible, and casually gnawed on it; I have scars that go to the bone and after seven years, I still don't have all the feeling back in that finger. Never will.
As a rule of thumb, I'd say that nobody who has been keeping reptiles for less than five years, and who has not kept at least five different species of lizards successfully, should even think about getting an iguana.
Best beginner reference: Iguanas for Dummies.
Worst: anything from T.F.H. They're the folks who were (dunno if they still are) selling books telling you to feed your iguana twice a week.
Note: Iggies are weird -- they have a digestive system more like a cow than like most reptiles -- and they need a steady supply of food passing through to keep it working. In the wild, they eat constantly, since they're basically sitting on their food supply. (plants) They must be fed fresh food DAILY. Getting an iguana-sitter is not easy.
Also, like all the other experts, I have to say: NO HOT ROCKS. They are an option for some animals, but iguanas are NOT one of them. Iguanas are baskers -- they're built to soak up heat through their backs. Their bellies are tough, so they can drag them over rough surfaces such as rocks without harm, and have very little feeling. An iguana can get third-degree burns from sitting on a hot rock. My vet has some nasty pictures of one of his patients hanging up as a warning.