is it safe?

is mdf safe to use for a cage if i use polyurathane to seal it really well and then let it air out for a week or so not finding PVC locally and it way to expensive to buy online 1/2 mdf is cheap though

MDF has chemicals in it that can cause issues. As well as not being able to deal with the humidity very well.

Look to see if there is a custom sign shop in your area, they might have sheets of PVC.

Other options would be polycarbonate (lexan or plexi-glass) ABS plastic, melamine, or plywood

ok new question is it safe to use real Oak to build a rack that has open top tubs? i just dont like the melamine look. i would polyurathane it so the humidity would not be an issue

Oak would be much better. Even when sealed it still isn't completely humidity proof. But should be ok, just make sure you let it air out before you put any snakes in it.

will do looks like i have a new project to start after my porch is done this weekend. i found some tubs about the size of 10 gal aquariums i think i am gonna use