RE: building boards
how flat is the suface you have now?
Take a florecent light bulb. The flattest thing you probably have in your house and rol it acrose the table. If it turns out to be percely flat then get some drywall and just screw it righ to the table.
If it is not percefly flat which it probable isn't then you'll need some else
The great planes building boards aren't bad. I get hollow core doors from my harware store for free. I screw it to a 2x4 frame and shimm it flat. It take alot of patients but with enough time and percicion you can get it flat. Remeber your wing is only as good as the surface your building on