Cut four 2-by-2-inch cedar boards to measure 20 inches long. These are the legs of the bench.
Cut four 1-by-4-inch cedar boards to use as the sides of the bench. Two of these sides need to measure 36-inches long and two need to measure 24-inches long.
Place two of the legs parallel to each other on a flat working space. Adjust them to 32 inches apart. Place one of the long side pieces across the legs. Slide the side all the way up to the tops of the legs. Screw in place with two 2-inch wood screws at each end. This is the front of the bench, repeat to make the back.
Set the front and back assemblies up on their legs on a flat surface. Adjust them so that they are 16 inches apart. Place a short side across the left front leg and the back left leg. Slide the board all the way to the tops of the legs and screw in place with two 2-inch wood screws on each side. Repeat on the left of the bench.
Cut a 1-by-4-inch board measuring 36-inches long. This is the center seat support. Slide the board in between the two short sides, parallel to the long sides. Center the support between the long sides. Screw it in place with two 2-inch wood screws put through the short sides and into each support end.
Cut six 1-by-4-inch cedar boards to measuring 28-inches long. These are the seat slats. Arrange the slats across the two long sides of the bench 2 inches apart. The ends of the slats should overhang the front and back of the bench by 1 inch. Screw each board to the long sides, and the support using 1 1/2-inch wood screws at each location.
Smooth out rough spots on the bench using medium-grit sandpaper. Be sure the top surface is extra smooth.