Cut 5½-inch-long by 1½-inch-deep notches in the tops of the posts. Lay out the site and dig holes for posts that form a rectangle 5 feet by 4 feet. Adjust the heights of the posts so the shoulders of the notches are level with each other. Tamp the soil or temporarily brace the posts in position.
Cut the ends of the 2 by 6 beams to a decorative profile. Seat the beams in the post notches and center them from side to side. Bolt the beams to the posts with two 5-inch carriage bolts at each joint.
Cut the cross braces to length as shown in the diagram and attach them to the posts by drilling holes and driving lag screws. Two cross braces attach to the tops of the posts; the third (longer) one goes on the end of the arbor opposite the bench, positioned 12 inches above the ground.
Cut the seat supports and back supports to length.
Position each seat support beside a post with the top of the support 16½ inches above the ground and one end flush with the outside of the post. Drill a single ¼-inch hole through the post and the support, then bolt them together with a 6-inch carriage bolt. Adjust the support so it is level. Drill a ¼-inch hole and add a second carriage bolt.
Bolt the front legs to the outside of the seat supports with 3½-inch carriage bolts, placing the legs 2 inches back from the front edges of the seat supports. Check that the legs are at least fairly plumb. Attach the back legs to the post with 3-inch screws.
Cut the 18-inch-long back supports so they taper from 5½ inches at the bottom to 2 inches at the top.
Align the back edge of the supports with the back of the seat and attach the supports to the post by drilling pilot holes and driving 3-inch screws. Attach the center back support by driving screws up through the seat from underneath.
Cut the back rail and backrests to length. Attach the back rail to the top of the back supports with 3-inch screws. (It will stick out behind the outside of the posts.) Screw the top backrest flush with the top ends of the back supports.
Attach the second backrest between the top backrest and the seat.
Cut the armrests to length and round their front corners with a jigsaw.
Use a router equipped with a 3⁄8-inch roundover bit to round the edges, then sand any rough edges. Attach the armrests to the tops of the legs with 3-inch screws, aligning the inside edges of the armrests with the inside faces of the front legs.
Cut the lattice supports to fit snugly between the posts behind the bench. Attach by drilling angled pilot holes and driving 3-inch screws. Cut the lattice panel to fit, and attach by driving 1¼-inch screws into the posts and supports.
Use a power miter saw or a circular saw to cut the ends of the 2 by 2 verticals and slats at a decorative angle. Using 3-inch screws, fasten the four verticals in place inside the cross braces on the side opposite the bench. Screw the eight slats on top of the beams. Screw the decorative corner braces in place. Finish the arbor with stain, or apply primer and paint.
Imagine sipping your tea or wine in the dappled light of your own backyard arbor bench, your favorite vine overhead.
Building a bench and arbor combo is in some ways less complicated than building a standalone bench. The arbor provides the structure, and the bench comes along for the ride with no complex angles or fancy joinery.