It is minimally OK for a veiled or panther, but I would not try to buy a larger adult if you have a choice. The larger the cage the easier it is to make the range of microclimates (temp and humidity) that chams need. That cage will be tall and fairly narrow and the cham may not make use of much of the "lower" parts of the cage unless there are a lot of healthy leafy plants all the way down. It will be harder to get the right size plants that offer enough cover. You may need some type of grow light hanging vertically down one side to keep your plants leafed out lower down. Chams are really different from other herps, even with experience. Most newbies with other herp experience say they had to learn a lot of new stuff for their first cham. Here are some good sites to read all about their care...you can trust the info on them.
http://www.chameleonnews.com
http://www.adcham.com
http://www.chameleonjournals.com
Also, stay away from the less expensive very young hatchlings. Irresponsible breeders sell them too young (don't want to feed them). These little ones are a lot more work, harder to cage temporarily, harder to feed, can be very sensitive to husbandry mistakes and nutritional problems, and are easier to stress and dehydrate. Some babies out of every clutch die for unknown reasons so if you get one too young that natural "culling" has not taken place...and your baby could be one of the doomed ones despite your good care. Look for a juvenile of about 3-4 months instead. You will pay more, but it will be worth it! Also, the cheaper veileds tend to have more health problems due to less-than-great care of their parents, the eggs, and hatchlings. Like a lot of things, you do get what you pay for most times.