You need to make a pattern. Measure you couch or chair, and make a diagram. Buy pattern paper which comes in long rolls. Try to find a book on basic pattern drafting or something like that to be a guide. Draw out each pattern. Pin the paper to the fabric and cut it out, then sew. Draping is another option, but unless you know what you are doing it could be a diaster. Take a patternmaking class if possible, I did.