Cut two pieces measuring 36 inches long from a 2-by-4. These 36-inch pieces will be the front and back seat braces.
Set the 36-inch 2-by-4's parallel to each other on their sides. Cut two pieces measuring 15 inches long from the 2-by-4s. These 15-inch pieces are the side seat braces. Place the side seat braces inside the ends of the front and back seat braces to form a rectangular frame.
Drill two pilot holes on the outside ends of the front seat brace and through the ends of the side seat braces. Insert the deck screws and attach. Repeat for the back seat brace.
Cut four pieces measuring 18 inches long from the 4-by-4 post. These pieces are the legs of the bench. Cut two pieces measuring 36 inches long from a 2-by-4 and one piece measuring 36 inches long from the 2-by-10 for the patio bench top.
Stain all sides, the end of the seat frame and the cut wood pieces using the latex exterior paint.
Place the patio bench seat frame on a flat surface. Set the ends of the 4-by-4 legs inside the corners of the frame. Drill two pilot holes on the outside of each corner on the seat frame and into the 4-by-4 legs. Insert the deck screws and attach. This will give you a total of four deck screws in each 4-by-4 leg.
Set the patio bench on its legs. Place one of the cut 2-by-4s on the seat frame, matching the board with the front and sides of the frame. Drill pilot holes through the 2-by-4 and into the seat frame. Insert deck screws and attach.
Place the other cut 2-by-4 on the seat frame matching the board with the back and sides of the frame. Drill pilot holes through the 2-by-4 and into the seat frame. Insert deck screws and attach.
Center the cut 2-by-10 between the 2-by-4s on the patio bench seat. Drill pilot holes through the 2-by-10 and into the seat frame. Insert deck screws and attach.