First of all, I'm assuming that you are referring to paper note books and not a PC. A PC would require special padding & reinforcement.
Lay out all the items you want to carry, stacking them how you think would fit in your bag & take some measurements.
Here's my 3 favorite free purse pattern sites, should be able to find something!
http://pursepatterns.com/free_bag_patterns.html
http://www.allpeoplequilt.com/projec...terns_ss1.html
http://www.allcrafts.net/sewing/pursesew.htm