To add to that, you want the cage area where the cham to get to be at least eye level. They want to be, as high as your head standing minimum, and ideally they will be above you.
A 30 inch tall cage, at 7ft to the top, is better for them then a 48 on the floor. IMO.
Ideally, you want the largest you can reasonably afford, but (IMO) a minimum of 24x24x48.
Personally, I'm building one 30x30x48 because that's the space I've been allotted on the Missus' plant table. The table is 30" tall, so another 36" (one foot from top of cage) puts the chameleon at 5'-6", which is just about my eye level. ?