custom cage, need input...lots of it

[Adam_Wysocki]

I am wanting to build an enclosure thats 3'x2'x *either 12" or 18"* which is my first question 12" or 18" tall? (by the way it's WxDxH)

12" would be better. Ball pythons feel more secure with lower ceilings.

I've read in a few places that plywood is good but sometimes has pine in it, and we all know pine isn't good for snakes. So after a few coats of Polyeurethane will it be safe?

Yes, as long as you let it air out for several days after the final coat. Melamine is better than plywood for beginner cage building.

Will the poly help prevent warping due to humidity and water spills?

Yes, coupled with a quality caulk along the joints. Melamine works well also.

How well will heat transfer through the plywood if I use undertank heat?

It won't. You should look into radiant heat panels for a wooden enclosure.

For the door, plexi or glass?

Doesn't matter.

-adam