material question for building a rack

Okay, so, i'm going to be building myself a snake rack. I have the plans pretty much ready, and i already got the wiring all done to add heat tape, but i do have a few very important questions.
Okay, so the frame will be made out of pine 1/2, and the sides, top, and bottom will be pine B/C plywood. I am using pine for those because the snakes will not come in contact with the wood itself. It's going to be a lidless system where i would just slide the tubs in. I'm not going to suspend the racks just make the shelves small enough so the snake can't slip out. If you know racks you know what i'm talking about.
So, question 1: What wood should i use for the shelves themselves? I was thinking birch or walnut, but it's nearly impossible to find and insanely expencive, where i am.
Question 2: If i stain and seal pine plywood will it still hurt the snakes? Or should i just go the safe rout and not use plywood near them at all?
Question 3: What kind of stains and/or sealants should i use on the wood?
Question 4: if i build the system and then stain and seal it will it change the dimenions and make it difficult to slide the reptile tub in and out?
Lots of questions, sorry! I just want to make sure i do it right so that i don't hurt the snakes.
Any, and all help, is greatly appreciated, thank you!

i built my rack out of melamine, 4X8 sheet at lowes for 30 bucks and they cut it all for you

then i just screwed it together, wound some flexwatt through it and thats all

need a picture?

oh well i went and dug it up any way
here ya go

http://i209.photobucket.com/albums/b...5/DSCI0101.jpg

I used plywood, and 2x4s and it is working well for me.:D

Awesome! Thanks guys!
As for melamine, i'm trying to stay away from it. I want to make this a semi-furniture quality to see if i can make a good rack system, after that i am going to build a fany-pancy one if i feel up to the challange. I would eventually like to add crown moulding and everything! I want to use melamine when i try to make vivariums with a door. Seems like melamine would be the best material for that and easy to clean. I like the rack system, though!
Stangs, what kind of plywood did you use? Was it pine or some other wood material?
Thanks for the help, guys!

I'm using plywood and 2x4s as well. :) My ply is 3/4" exterior roof/wall grade. Working on it now and so far so good.

ok, so here is my biggest concern...
Plywood has pine in it. Pine is harmful to snakes. If i use plywood with pine in it is it okay? If i seal pine or pine plywood is that alright too?