Cut three crossboards for mounting the tabletop out of one 2-by-4, making each section 26 inches long, then nail eight 2-by-4s to the crossboards. Place one crossboard in the middle at the 4-foot mark in dead center and place the other two 4 inches from the ends, ensuring 1 inch of overhang on both long sides of the table.
Cut four legs for the table using two 2-by-6s by cutting at a 60-degree angle. Use a square to ensure that the cut is 60 degrees on top and bottom, marking the length at 33.5 inches on both sides. Cut the remaining 2-by-6s each to 5 feet in length.
Flip the tabletop upside down and mount the legs to the inside of the outermost crossboards, leaving a 3.5-inch gap from the outside of the tabletop. Then drill eight 3/8-inch holes to mount each leg (two bolts per leg). After you drill the eight holes, countersink the nuts and washers by drilling a 3/4-inch hole with the spade bit on top of the 3/8-inch holes on both sides. Insert the bolts and fasten them with nuts and washers on the inside of the legs.
Attach the two 5-foot 2-by-6s as a mount for the seats (that you cut previously) to the legs on both sides, making them horizontal to the floor and placing them so that the seat will be 18 inches from the floor. Use another two bolts per leg when attaching the seat mounts and countersink the nuts and washers on the inside of the each leg.
Cut two diagonal braces from a 2-by-4 at a 17-degree angle using the square. Make both pieces 44 inches long. Note that you may have to adjust this measurement slightly by sanding or cutting to ensure that the diagonal supports are cut to a precise fit. Attach the braces to the center crossboard in the center and nail them offset slightly from one another and run them down to nail them into the seat mounts.
Nail the remaining two 2-by-4s in between the seat mounts flush with the top, making a brace and support for the seats. Then attach the 2-by-10s to form the seat by nailing them into place on the seat mounts and brace. Make sure the legs are square and even before nailing the seats in place.
Sand down the rough corners and tabletop using a palm sander, then finish with an outdoor sealant or varnish as desired. Allow the coat to dry, then reapply for better protection from weathering.