I'm a huge fan of out side sun cages. I'm of the opinion it is the best way to expose your chameleons to UV rays. For me you cannot go to big with suncages as well. If you are worried about ants, if you have got a stand, put each stands legs in a bucket of water.
The main concern is as being outside the chameleons can be tempted to escape and nose rubbing and screen climbing can be a problem. You may want to look for plastic covered screen to build your sun cage with.