I just built a set a couple weeks ago. It was a pretty easy setup.
2 boxes. Each box has a top and base. The top is 1'x4'x1" with 3 4" diameter holes evenly spaced across the 4' length. For the base I used a 2x6 and cut it into pieces to make a 4 sided box (no top or bottom) that was approx 8"x3.25'. Used wood screws to attach the top to the base. I also added a 10' rope attaching the 2 boxes so they can be evenly spaced each time you play a round. For that I drilled a hole in the front edge of each base and threaded it with some heavy cord. Tied knots on the inside of the box to keep the rope length constant.