Okay been a while since i've posted on this subject.
Birch plywood will give you a much smoother finish on your cage than pine will. The home depot here actually carries a birch/rosewood mixture called Homer Ply that only runs about $25/sheet. Check into that, it'll give you a finish very simliar to birch, and much better than pine. Any plywood will be fine to build your cages.
Painting - PRIME IT! I can't stress that enough. What I use is the Behr interior primer. It seals your wood up and makes it ready for paint.
If you want a good long durable finish, use an oil based primer and paint. However, you're looking at about 2-3 months before you cage will be useable. I'd just go with a latex paint. It's water based and will stop smelling within a couple weeks. However, MAKE SURE you are getting a latex topcoat and primer, not an oil based primer. Use the Behr primer in the purple can and you'll be fine on a latex primer.
Use Behr interior SATIN ENAMEL finish. You go to home depot they also have cheaper satin enamel finishes, some are 100% acrylic and some are a poly vinyl acetate mixture (PVA). Acrylic and PVA are the types of glues in paint, essentially. Acrylic is much more durable and holds better. You see a $10 can of 100% acrylic and a $20 can of 100% acrylic, there are a lot of differences. One in this sense, however, is the $10 can may have about 1/4 cup of acrylic, the $20 will have a full cup. They're both 100% acrylic, but this is how they market it to screw you over into buying the cheap stuff.
Also, looking at the enamel finish. Enamel is nothing more than the way they mix the ingredients in paint to give it a hard durable finish. I like Behr, used it to paint my whole house with. Satin what I use in cages. It gives a very minimal sheen. USE 2 COATS FOR THE INTERIOR OF A CAGE. you'll thank me later for that.
However, with an enamel paint, you can not touch this up. Reason is the shine won't match the rest of the deal. Other than that, it's fine.
Give it about 2 weeks to outgas (stop smelling.)
Uhm... i think i've pretty much told you what you need to know on the paints, and then a lil more also 
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Chondros and colubrids... my 2 favorite types of snakes!
"Life is hard. Life is harder if you're stupid." - John Wayne