I made two cajons when I joned slms. One was big enugh to sit on and a handheld one. The big one is still at my storage as it got a bit damp when i left it outside (for moths by accident) and the small one is cute, but extremely impractical. I used plywood for the big one with 9mm thick walls and front and back if I remember correctly was a 2mm laseply, the bass hole I lasercut in shappes of a water ripple which i also engraved on the rest. I got a snare that i never fitted.
The small one was from a 3mm plywood and a veneer stretched over the front.
Would be nice seeing what you make, mine was more of a woodworking learning project that ended up good enough, but i am sure the tappa could be done more precisely.