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I wanted to build a top for my tank using plexiglass to retain humidity. I wanted to cut out circles in the plexiglass for the heat lamps. I was planning on gluing a square sized sheets to where the lamp cut outs in the plexiglass are located to prevent from having holes for the monitor to escape. I will of course make hinges or something to prevent the top from getting opened. Does anyone think this is a good idea or have seen it done before? Also, is it possible to cut circle shapes out of plexiglass? Last question is, what type of adhesive glue can is recommended to glue the screen to the plexiglass? Thanks a lot for your response.

I don't think it's a good idea. With the heat lamps in close proximity to the acrylic you will likely cause warping. If the cage is high humidity this warpage could be severe.

I don't know what I'd recommend.
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Current snakes:

0.0.1 Gonyosoma oxycephala - Java locale (green)

1.2 Gonyosoma oxycephala - Jave local (green)

2.2 Gonyosoma janseni - Seleyar locale (all black)

1.2 Gonyosoma janseni - Celebes locale (Black & Tan)

What I've been doing is using a screen top and covering up about two-thirds of it with a piece of plexi, leaving the other third open with the dome light above it. I lift up the piece of plexi to spray.

Recently I picked up a piece of that thin clear plastic that is used with flourescent light fixtures which is cheaper and light weight. I will cut a piece to size then use silicone or hot glue to attach it to the frame of the screen.

the only thing that could cause plexiglass to 'warp' is the heat from the heat lamp bases;plexiglass is non-permeable so water/moisture won't effect it.like you said you could have a square template to mount the fixtures to,and just cut out a hole i'd say at least 6 inches from the fixtures;inside that hole is where you can mount/bolt the templates to the plastic.
for circles in plexiglass or anything else,a rotozip is a nice tool,looks and works like a jigsaw/drill hybrid.the bit it uses is basically a drill bit with tapered edges.
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"with head raised regally,and gazing at me with lidless eyes,he seemed to question with flicks of his long forked tongue my right to trespass on his territory" Carl Kauffeld

i would frame up a would cover use plywood on the top and build around the edges so it fits snug, then take your heat lamp fixture trace the circle on the top and cut it out half inch bigger with a sabre saw. then get some 1/4 inch screen and cut it to overlap the hole on the inside and staple it on that way your light sits on the screen. it works good for me....

Thanks for all of your responses. One question though...it seems like I can use plexiglass as a top or plywood. Which one has its advantages or which one overall would be better? Thanks again!

the only thing that could cause plexiglass to 'warp' is the heat from the heat lamp bases;plexiglass is non-permeable so water/moisture won't effect it.

Another poster here supplied a link to a plastic site saying that acrylic can indeed warp from humidity differentials.

I still think heat is the biggest contributor, however.
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Current snakes:

0.0.1 Gonyosoma oxycephala - Java locale (green)

1.2 Gonyosoma oxycephala - Jave local (green)

2.2 Gonyosoma janseni - Seleyar locale (all black)

1.2 Gonyosoma janseni - Celebes locale (Black & Tan)

>>Another poster here supplied a link to a plastic site saying that acrylic can indeed warp from humidity differentials.
>>
>>I still think heat is the biggest contributor, however.

Chris, I too think heat differential is major cause of warping but I used a 1/2 inch thick piece of acrylic to make a top [with ventilation holes] for an unheated leaf cutter ant tank. The near atmospheric saturation humidity levels in the tank caused the acrylic to warp a full 1/4 inch or more side to side.
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Matt Campbell

"I only went out for a walk and finally concluded to stay out till sundown, for going out, I found, was really going in." John Muir

>>plexiglass is non-permeable so water/moisture won't effect it.

Heat and humidity WILL cause plexiglass/acrylic to warp. In fact, the worse the differential inside the cage to outside the cage, the worse the warping will be. Also, thicker acrylic will warp worse than thinner material because the heat and humidity differential across the thickness will be greater. I've built a number of cages and used acrylic for tops, doors, etc. and I have yet to build something that didn't warp. The worst instances were on cages that were very warm and humid [ie. tropical species], although I've had warping issues with species kept hot and dry. Again, it all boils down to temperature differences inside the cage compared to outside. Overall, I've discarded acrylic as a material for use in cages because it's far too unstable. Supposedly some brands of polycarbonate such as Lexan are less prone to warping but still overall do not make good materials. To build the top the poster is describing, I'd use some other type of material - perhaps a combination of wire/glass/wood.
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Matt Campbell

"I only went out for a walk and finally concluded to stay out till sundown, for going out, I found, was really going in." John Muir