Good Morning,

I use glass. Either cheap pcs from the person that drills my tanks or from cheap picture frames.
ie Michael's, Kmart? I recently picked up a cheap frame (24x36" ) at Kmart for $5. This is much , much cheaper than the glass guy. It's thin, but I believe that is an advantage for the tank tops rather than the "special stuff" that block uv rays. I never place any heat source directly on the glass.

I have my tree frogs in exo terra tanks.
Most of the screening/top has been pulled w/ the exception of a one section on each that I place a dual-fan. The the fan runs ( on a timer) a few times a day (for 15 min) ; it pulls the air...ut . Naturally, the fan runs more in the summer than in the winter.

If you have exos. it is very easy to pull the screen and replace it with glass. I hold the glass in with "Marineland" aquarium sealant. However, for tree frogs, you don't want to seal it up completely. I use the cheapest glass I can find. One w/ out any uv protection stuff, so lights an penetrate as much as possible.

If you want to..... post a photo of your tank ( and tank top ). Let's see what other ideas members have.
There are lots of very creative people here- to help !

Lynn