Start by cutting four of the 2x4s in half, so that each piece is 48 inches (1.2 meters) in length. Cut an additional 2x4 in half and take 8 inches (20 centimeters) off of just one of those pieces so that you have another 48-inch slat and one 40-inch (1-meter) board.
On another 2x4, mark off 40 inches and use that piece to cut two trapezoids, each 20 inches (50 centimeters) in length at the base and with 15-degree angles on each side. Use the rest of this 2x4 to cut three parallelograms that are 17 inches (42 centimeters) in length and also feature 15-degree angles.
Cut your seventh 2x4 into four pieces. The first is a 31-inch (79-centimeter) long slat with a 90-degree angle on the left side and a 15-degree angle on the right side. Make the next two pieces trapezoids that are 23.75 inches (60 centimeters) at the base and have 15-degree angles. The last piece should be a 17-inch long parallelogram, also with 15-degree angles. Finally, saw the last 2x4 into another 31-inch long board with a 90-degree angle on one side and a 15-degree angle on the other.
Now you're ready to start putting the bench together.