Use this basic book idea and expand it even further. Add plain pages instead of envelopes, lengthen the accordion folded spine to accommodate even more pages/envelopes, use a different size envelope or square envelope and change the size of the book to match, find another material to use for the covers or pages, etc. The possibilities go on from there!
Craft Projects Ideas with Old Books. Repurposed Items can can used to make creative home decor. Check out these DIY Projects Tutorials for Books for Ideas >> http://diyready.com/diy-projects-made-from-old-books/