The amount of ventilation needed depends on the species being housed, in this case I would go with a pair of 2" round vents in the top and a front vent of about 3.5".
Thanks for this info! The vent I have are about 8 inches in diameter, is this too big? They're made of some sort of thin metal, probably aluminum.
0.0.2 Litoria caerulea
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"The gallows are no place for the stubborn//Just you and your lover as a dark souvenir" - Bad Books, Pytor