The first step to building your own cornhole game board is to cut the pieces for the frame. You'll need two pieces of 1x3 cut to 47 inches and another two cut to 21-1/2 inches in length.
Butt the two 21-1/2" pieces into the sides (one at each end) of one of the 47-inch pieces, and attach each with two 1-5/8" wood screws. Follow suit with the other 47-inch piece, attaching it to the opposite end of the 21-1/2" pieces to form a rectangular box. This is the basic frame to support the board.
TIP: To avoid splitting the pieces, be sure to pre-drill the holes along with a countersink to accommodate the head of the screw.