Hi Lori,
I use to use 1/4" Plexiglas for my cages now I use 1/4" tempered glass for my cages.
Plexiglas has to much give in them so I would add aluminum 1/4" u channel on the side edges. I would just use any good glue for this such as liquid nails.
Eddie has a very good idea there too.
But if you have 20" or more in height the boa or any good size snake can squeezes out between the two pieces of Plexiglas.
The aluminum gives the edges some reinforcement that will help stop the Plexiglas from bowing out.
Here is a picture where you can see the u channel some what.

[addsig]
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