Determine the dimensions of your sofa frame. Reference a furniture magazine, which often details the dimensions of the sofas they offer. Consider using the frame of an old unwanted sofa as a guide or template. Dismantle it and reuse the parts to help you build the framework.
Acquire 2-by-4 lumber to build the frame, if not borrowing and reconstructing the frame from another sofa. Form a rectangular shape to be used for the seating area. Screws can be used to secure the boards where they meet.
Assemble 2-by-4s at the desired height and measured to fit the width of the couch for the back piece. Secure the boards where they meet with screws. Angle the back away from the seat section of the frame at the desired angle. Secure the back piece by screwing slanted L brackets, or triangle supports, into the frame.
Determine the desired size of the arms of the couch. Assemble 2-by-4s in a square or rectangular shape on either side of the frame. Use bolt screws to secure the arms to the frame.
Determine the desired length of the legs for the couch. Measure them to size and cut them with a hand saw. Position each leg at a corner of the couch and inside the frame. Use screws to screw the legs to the inside of the sofa frame.