put book on fabric , 2" from edge. Fold so book is enclosed and fold is the bottom of the bag. Leave 1/2" at sides and 2" at top. cut fabric. Take book out. Fold up, sewn on two sides, hem the top, attach straps. takes 15 minutes to make.
For those who like pictures, a tutorial can be found at ehow here , screenshot:
If you attach the straps lower, the top of the bag will naturally fall into the bag and make a closed look, because there is extra fabric at the top.