I did the same thing. I used metal window screen for the outside layer, and a plastic hardware cloth type of thing for the inside. I just used the screen on the top, but then Orion decided to go exploring up there and hurt two toenails, and I ended up using the plastic stuff anyways. I was worried about it melting, but if you think about it if it is hot enough there for the plastic to melt, andyour cham can get there, than you have more to worry about than just toes catching... it will burn your cham. The plastic is pretty tough, so it should be ok, as long as your lamp is suspended off of the top of the cage. Or, you can use screen to hold up the lamp, and use the plastic as a roof a few inches down from the screen to give space to keep your cham away from the light. 
Also, you can get PVC coated 1/4" hardware cloth. Most places you have to special order it in 100' rolls, so it's mostly just worth it if you are going to make another cage now or down the road you can save it. That is your best bet.