The equipment you need to house them and keep them at the right temperature can cost a lot and take up a lot of space. Large reptiles can defecate copiously and messily, and need a lot of cleaning. You need to have a special fascination for reptiles before buying one, enough of an obsession to put in the effort needed to keep them healthy. You'll also need to have reliable friends, neighbours or family members who'll help take care of your herps while you're on holiday. Some reptiles are easier than others, so if we haven't put you off yet, try starting off with the smaller and more placid types, like bearded lizards, and some of the chameleons and geckos.
Green iguanas are handsome creatures, but they can grow up to six feet long, and be aggressive.
Think of what you're likely to be doing over the next few years, and whether you can take your reptile with you, or rehome it if you can't. Tortoises can live longer than most humans, and red-eared terrapins can live for 30 years, but both are relatively easy to rehome. Burmese pythons can live from 18-25 years, and royal pythons nearly as long. Corn, rat, king, milk and garter snakes can live up to 15 years. You need to know what you are buying, so you don't accidentally buy one of the more challenging species, or a reptile that is illegal to keep in Britain without a dangerous wild animal licence, like a caiman.