Lay two planks of 20-inch, 2-by-2 lumber 8 inches apart on a work surface. Measure up 11 inches from one end of the 20-inch planks and insert a piece of 8-inch 2-by-2 lumber between the 20-inch pieces. The 8-inch plank should be at right angles to the two 20-inch planks, making an “H” shape.
Drill two pilot holes, sized for 2 1/2-inch screws, through the sides of the 20-inch planks into the ends of the 8-inch plank, then screw in 2 1/2-inch screws into the pilot holes to secure the 8-inch plank in place. The 20-inch planks are the back legs and back of the chair.
Lay two planks of 11-inch 2-by-2 lumber on a work surface, 8-inch apart. Insert a plank of 8-inch 2-by-2 lumber between the ends the 11-inch planks, so the 8-inch plank is flush with ends of the 11-inch planks. Secure the 8-inch planks as you did the first one to the back legs. The 11-inch planks are the front legs.
Stand the front legs upright with the 8-inch plank up. On the face of the legs adjacent to the 8-inch plank, abut another 8-inch plank so that a corner is formed. Attach the second 8-inch plank to the leg, then repeat on the other 11-inch leg so that there are three 8-inch planks attached to the legs in a “U” shape when you look from the top down.
Stand the back legs upright, with the 8-inch plank closest to the ground. Abut the front leg unit, with the two sticking-out 8-inch planks flush on the back legs. All the 8-inch planks should form a square at this point, with the legs in the corners of the square. Secure the ends of the 8-inch planks abutting the back legs as you did with the other 8-inch planks.
Position a 12-inch 1/2-by-2 inch lumber slat between the back legs, about 1/4 inch below the top of the legs. Secure with two 1-inch screws through each end of the slat into the legs. Attach a second slat 1/2 inch below the first to complete the backrest of the chair.
Evenly space four slats across the top of the square formed by the 8-inch planks to make the seat of the chair and secure in place the same way you did the backrest slats. Complete the chair with a coat of the wood finish of your choice.