jstyle13-
Just FWIW, a hunk of drywall isn't a bad working surface but is a little hard on the fingers when pushing a lot of pins in. Just note that there is normally a taper on the "paper" side that starts about 3" away from the long edge. This is so that when the seams are eventually mudded and taped, the end result is a flat wall. You will want to cut this taper off and use a clean edge for your building board. Either that or your building area will get slightly smaller.

Welcome back to the hobby. Hope all goes well.