The biggest problem with glass terrariums is that they usually are not big enough for the bigger species of chameleons, and if they are big enough they're usually extremely heavy and expensive. If you're already concerned that it's not big enough now would probably be the best time to go ahead and return that one and get a more appropriate size cage, and screen is generally preferred because they come in big enough sizes and keep air circulating well. An adult veiled chameleon will need a cage at least 18x18x36" tall, and bigger would be better. The little glass terrariums are great for smaller species like pygmies, but not the best for the bigger species.
Kati and Veiled - arguing about trivial details doesn't help newbies feel welcome. Just answer their questions next time and duke it out in PMs.