Start with the ends
1. For each end module, cut two 84-inch-long 4-by-4 posts; one 29-inch 2-by-6 top cross-brace; one 29-inch 2-by-4 table brace; and one 44-inch and one 67-inch 2-by-6 bench beam. On the bottom ends of each 44-inch and 67-inch 2-by-6, cut off small triangle shapes―measure 2 inches up and 3 1/4 inches in from the corner―that will match up with depth of the 2-by-4 bench sides.
2. Space the 4-by-4 posts 22 inches apart on a flat work surface. Overlay the 29-inch 2-by-6 cross-brace flush with the top and sides, check squareness, and attach with four 2 1/2-inch deck screws per post.
3. Mark points 15 1/2 and 28 1/2 inches from the bottom on each post, and attach the 29-inch 2-by-4 table brace so its top is flush with the upper (28 1/2-inch) mark, using two 2 1/2-inch screws per post.
4. On the longer (67-inch) 2-by-6 bench beam, mark points 19 inches in from each end, and on the shorter bench beam, mark points 7 1/2 inches in from each end. Use those marks to align the boards with the outside edges of the posts and clamp the boards in place. Their tops should align with the 15 1/2-inch mark.
5. Where the longer bench beam meets the center of each post, mark one point 1 1/2 inches from the top edge and another 1 1/2 inches from the bottom edge. Drill 1/2-inch-diameter holes through all three boards at those four points. Insert 7-inch carriage bolts, add washers and nuts, and tighten with a wrench.