Here's a solid portal topped with a bit of elegant whimsy.
1. MAKE A CARDBOARD TEMPLATE for cutting the 2x6s. Draw a rectangle 5-1/2 inches wide and at least 17 inches long to represent the 2x6. With a compass, draw arcs from the points shown. Cut the template out of the cardboard with a utility knife. Use a heavy-duty jig saw to make the cuts.
2. BEGIN FRAMING by digging postholes deeper than the frost line. Add 2 inches of gravel and set the posts. Connect the posts with temporary bracing, check for plumb in all directions, and pour the concrete. Allow five days for the concrete to set and cure.
3. CUT ALL THE POSTS LEVEL with each other, about 9-1/4 feet above the ground. Attach the four lower flying pieces to the sides of the posts with 3-inch galvanized deck screws. Add 1x2 trim beneath each, using 6d finishing nails. Either butt the ends as shown, or miter the corners.
4. LAY OUT THE UPPER PIECES so they are evenly spaced, and attach by predrilling holes and driving 3-inch deck screws at an angle. Top the structure off with the 1x2 pieces, using 1-5/8-inch screws.
5. CUT THE LATTICE SHEET so that it overhangs the braces evenly at the top and bottom, and attach it with 1-1/4-inch screws. On the inside of the arbor, attach the 1x2 nailers and 1-5/8-inch screws, and screw the lattice into the nailers.
Here's a solid portal topped with a bit of elegant whimsy. Heavy 6x6 posts set in concrete provide firm support for the specially cut flying pieces on top, making a substantial entryway or focal point for your landscaping. While the most demanding task will be cutting the shaped ends of the flying joists, a person with average carpentry skills can produce this impressive garden feature. Allow a couple of weekends for the project.
Use rot-resistant wood for this project such as redwood, cedar, or pressure-treated lumber -- there are plenty of places where moisture can settle. If you find that you cannot get 6x6s in your chosen material, use a protective stain to blend the pressure-treated lumber with cedar or redwood.
Plan on digging the postholes and setting the posts on the first weekend, allowing five days for the concrete to set and cure. Paint or treat the pieces before you assemble them-perhaps while the concrete is curing. You will need a heavy-duty jig saw or band saw to cut the curved ends of the 2x6s. When cutting through the 6x6 posts, make the initial perpendicular cut with a circular saw, then finish with a handsaw. Have a sturdy stepladder on hand. Draft an assistant to help install the top pieces.