Set the blade angle on your circular saw to 45 degrees and chamfer the bottom edge of the two ledger-board sections.

Notice the clamped board that serves as a straightedge.

To cut the dadoes in the ledger board, use a router outfitted with a straightcut bit set to a depth of 1/2 in.

Notice the two scraps of wood that are temporarily screwed to the ledger that serve as guides.

Use a jigsaw to cut the inner and outer brackets as shown in the drawing.

Note that one outer bracket per arbor half is not notched, but instead it butts against and overlaps the end of the ledger board so that there is no exposed end grain.

Notch the main supports to a depth of 3/4 in. by ganging them together and running them repeatedly through a table saw.

Use the saw’s miter gauge to support the stock. (If you don’t have a table saw, use a circular saw to create the notches.)

Attach the brackets to the ledger board using two 3/8-in.-dia x 5-in. coated washer-head lag screws for each support beam.

Countersink the heads so that the ledger board will rest flush with the house.

After cutting the end profiles of the crossbeams and notching them to a depth of 3/4 in. as shown in the drawing, attach them to the brackets using 2-in. stainless steel screws.

Then use 2-in. outdoor-rated finish nails to fasten the 1x2 strips in place atop the crossbeams.

Once you have moved the two halves of the arbor to the installation site, clamp them together and use 2-1/2-in. tan deck screws to fasten them — remember to countersink the heads for the best appearance.

Round up some friends to help lift the arbor into place.

While they’re holding it, drive 3/8-in.-dia. x 5-in. coated washer-head lag screws through the ledger board and siding into the garage door’s header.

Use two screws placed every 24 in.

Attach a final 1x2 strip to cover the seam where the two support beams are attached together in the middle of the arbor