[Griff]

The pieces parts were pre-cut, Pete just glued, nailed, and painted them. Box joints are not that hard though and they can be cut a number of ways. The internet can be your friend on this. Find a system that matches the tools you have. Using a square, I'd probably lay out the fingers in 1" increments making sure to offset the fingers for the sides vs the front and back. Then use a hand saw and a chisel to remove the wood. Just take your time and keep everything nice and square from start to finish. Or you just butt the boards together and screw them...