Building the bench takes about half a day, and finishing it adds a few hours. You don't need expert skills or fancy tools, just a table saw, circular saw, drill, jigsaw and router. The heads of the screws that fasten the seat slats to the base are covered with wood plugs made using a drill-mounted plug cutter that's available by mail order.
I made the bench out of dimensional cedar from a local home center. Other options include fir, redwood, white oak or pine (if you paint it). After construction I applied clear exterior oil-base finish, but you could leave the wood unfinished and let it age naturally if you prefer.
The biggest challenge I faced was finding boards of a consistent color. Though I was extremely choosy when selecting lumber, I had to use different-color boards. My solution was to make the colors appear symmetrical on the finished piece. I used one board for the legs and seat supports (A and C), one for the cross-support and center seat slat (B and D), and the third for the outer seat slats (D).
It's critical that you make the angles on the top inside corners of the legs exactly 90 degrees or you will have trouble assembling the bench. Double-check the angled cuts with a combination square, and fine-tune the angles with a belt sander, stationary sander or hard sanding block.
Make the base parts
Cut the legs (A) to size (see cutting list in the PDF below). Lay out the leg shapes (see illustration, also in the PDF). First cut the 75-degree ends of the legs on a table saw (photo 1). Then cut the inside upper edges of the legs with a circular saw or jigsaw (photo 2). Finally, cut the inside lower edges.
Cut the 75-degree bottom ends of the legs using a table saw and miter gauge or a circular saw and straightedge guide.
Cut the inside edges of the legs. A speed square clamped to the legs acts as a guide. Accuracy is critical with this cut. The resulting top inside corner must be exactly 90 degrees.
Cut the cross-support (B) and seat supports (C) to size. Lay out their end angles and notches as shown in the illustration. Cut the notches (photo 3); then cut the end angles. The cross-support and seat-support notches should interlock tightly. Draw and then cut the cross-support arc (photo 4).
Make a series of cuts to create the seat-support notches. Break out the waste, and use a file to smooth the bottom of the notch. A stop block is used to align the blade with one side of the notch.
Use a flexible wooden batten to draw the cross-support arc. A nail holds the batten at the top of the arc, and blocks are clamped to hold the ends of the arc. I used a 1/8 x 3/4 x 40-in. piece of oak for the batten.
Assemble the base
Cedar is soft, so you must be careful not to overdrive the screws, and there's no need to drill pilot holes for most of them (see photo 5 for an exception). It is helpful to drill clearance holes for the screws. A clearance hole is the same diameter as the screw and is drilled completely through the part that the screwhead will press against. The clearance hole helps the screw pull the parts tight.
Secure the legs to the cross-support with 3-in. deck screws. Drill angled pilot holes to help guide the screws through the cross-support and into the opposite leg.
Finish sand the base parts. Screw the seat supports to the crosssupport nat the notch intersections. Screw the legs to the seat supports; then screw through the crosssupport into each of the legs.
Make and attach the seat slats
Cut the seat slats (D) to size. Drill counterbore and clearance holes for the seat-slat screws. Use a chamfer bit to rout the outside edges (photo 6). Finish sand the seat slats; then screw them to the base. Make 16 wood plugs (photo 7); then glue them in the counterbore holes (photo 8). Make the plugs long; you'll trim them after glue dries.
Rout the chamfered outside top edges of the seat slats. Wood blocks clamped to the edges will protect the ends from "blowing out" and stop you from accidentally going around the corner to an unchamfered edge.
Make the wood plugs using a selfcentering plug cutter. Use a fast drilling speed, cut more plugs thann you will need, and pop them out with a screwdriver.
Apply glue and tap the plugs in the counterbore holes. Let the glue dry; then trim off the excess using a flush-cut saw or belt sander.
Ease all exposed sharp edges with sandpaper. You can leave the wood unfinished, apply clear exterior oilbase finish or add some color by using an exterior wood stain typically applied to cedar decking.