I started with a 1" x 8" x 12' piece of pine and had it cut into 41-inch sections (at Lowes - they did it for me!). I used a 1" x 6" x 15" piece of wood to make the horizontal slat.
I fastened them with 1 5/8" decking screws - regular screws would have caused rust. Next, I sanded them down - focusing on rounding the corners and raw cut ends. Finally, I applied a semi-transparent decking stain (Behr's Boothill Brown) to give it a weathered look... my goal was to match our wood shake roof.