Thats the great thing you can never make the vents to big in my book cause you can always cover some up later but its hard to make vents bigger in a cage with a resident.
I use 2"x12" register vents from the box stores for mine and simply cut holes that I edge sealed later and mount the vent with liquid nails and a few machine screws.
I also vent the top of my cages to let out excess heat but some like to vent the bottom, and for a species like a burmese I would suggest following that practice. The Urates put off some pretty strong fumes. I wouldn't recommend placing the vent lower than a few inches so you don't get liquid waste spilling out of the cage.
Best of Luck
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Jeremy
"I am become death, the destroyer of worlds" July 16, 1945 Robert Oppenheimer
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