Any wood will do fine ad long as it's not treated. However cedar and pine have been known to cause respiratory problems. As for sealing, you don't have to. I just used laminent flooring.
If you use plywood I'd highly recommend finishing it with a veneer or sheet laminate. It'll give you a more finished look, reduce the odor absorption, and make it easier to clean.
Eric is right. But don't make the same mistake I did and velcroe the laminent to the enclosure, I thought it would be easier to remove and clean but the heat ended up making the flooring warp and bend.
Check out Sandeply at Home Depot. It has a fairly smooth consistent finish. I've used it for all my enclosures and sealed with polyurethane sanding in between. It doesn't show the grain like standard plywood so it looks like veneer.
I used Min-wax on my DIY tank I finished th e other day (A custom 60 gallon extra long). It dries fast too. The toxicity isn't a problem either once its dry....well unless your beardie eats wood, then you could have a problem :lol: I'll put up pics soon of my self dubbed "60 gallon extra long lizard party tank". I built it for my 15 week old beardie, but of course he hasn't graduated to it yet. The real important thing is making sure that plywood is sanded good. When I was working with it I got half a dozen splinters doing it (don't worry I got them all out ) so I can imagine it could do the same thing to the beardies belly, so I sanded that bad boy good. You could even stain the wood if you don't like the natural color, I did to better match my room. Just make sure the stain is TOTALLY dry, and its fine. Also how are enclosing the viewing part of your cage (AKA the part you see your dragon through). I did my in fine laminated chicken wire for now. I know what your thinking, "chicken wire, the crickets will just hop through." I have a seperate feeding tank after being with crickets escape everything from glass aquariums to cricket keepers inside another box! I might switch to screen I might not, its not a problem for me, because of the feeding tank. I keep my crickets in a DIY designed live prey escape proof tank below my feeding tank, or feeding arena if you prefur .