If you haven't seen the Disney movie, "Enchanted", you should. I love the scenes where Giselle has made dresses from the drapes, bedspread, etc. Here is my "enchanted" purse from this old worn-out jumper:
Pattern here. Mine is 17" wide and 19" tall. I put a pocket in one side for my phone and two pens. I just made a square and then stitched it down on 3 sides plus two lines both one inch from the vertical sides for the pens.