Plenty big
I had plexi with flexwatt underneath with rubber feet from Lowes inside one of my diy cages hooked up to a thermostat of course.
That thick of wood will make your cage very heavy, like mine was and it was only 32". Remember that it should be able to handle humidity and any spills that might happen.
Btw, have you priced out the cost to build (unless you have the stuff sitting around already)? There are a few shows where you can get plastic or wooden cages in PA for 100 and up, $150-200 for a 4ft is typical.
Having a sense of accomplishment is great only if its cost efficient![]()