Here is the pattern for the faux leather rucksack I made. (add a waist belt?) You can see the scale at the bottom right. If you make sure the red line is 10 cm when you print out the pattern, all the pieces will be th.
A Chic Leather Backpack - this would be great for carrying a medium sized portfolio
Tote converts to backpack - maybe use grommets for fabric version?
Leather backpack draft/sketch/possibly pattern. instructables, impressive photos of diy leather rucksack