In terms of the open sides, I don't see it being an issue as I know many people who use "ladder racks" that are built in this stile and don't have an issue with them as long as you have flexwatt controlled by a thermostat. I don't have my receipt but really it could be done with any type of wood. Although depending on what type of animal you're housing, how much humidity it needs you may need to seal it. I can find out the type of wood the next time I'm at home depot. Really any type of wood will work, although I'd avoid wood that looks layered when you look at the side (where it's about an inch think) if it looks like it's layers I'd avoid it. Really you could use pine, poplar, oak, whatever you want that's in your price range.
Sometime in the near future I'm going to be picking up some oak I believe and building a "Hidden Display Rack" (ironic huh?) basically since we're running out of room to keep our herps we're going to build a quarantine rack for our living room but we don't want people to be able to see the snakes exactly so we're going to build a display rack that looks more like an armourer or tv cabinet with the doors closed and when you open it the tubs and such will be inside. We have also toyed with the idea of buying some kind of tv cabinet and just converting it to a rack. We'll see how that goes, anyway, hope this helps and I'll get you the info on the wood in the next few days.