I think you'll be way happier just buying a decent sized plastic enclosure, but if you really want to build with wood, yes you can use plywood you'll just have to protect it against moisture. The one product someone will likely recommend that I would steer clear of for this is drylock, very rough texture which makes cleaning it near impossible. It's rough enough that superworms could climb straight up it... never again for me! I would use something that leaves a smooth surface. Also IME it takes a lot longer for fumes to dissipate than whatever the label tells you. so plan well in advance and figure out where you'll going to leave all this wood while it is evaporating fumes into the air, definitely don't want that in your reptile room until it is cured. Finally, wood is extremely heavy so put the thing together pretty close to where you want it to stay and hope you don't have to move it anytime soon.
These are the plans I've used and are the best I've found. If you decide that's too much of a pain, I've been very happy with the apcages been stacked for years with no issues at all. Radiant heat panels are great, I use them in my snake enclosures but none of mine are very tall enclosures so I'm not sure how how reach they have for height as I've never tested. I do believe they are considerably less drying than heat bulbs.
Hybrid Mode
