I've been wanting to do this since I saw an Alice in Wonderland book made into a purse on Etsy. Sadly, though, I was unable to get my hands on a cute hardcover, so I had to settle for an ugly hardcover book, which I revamped. It's about six inches wide, nowhere near as large as the picture makes it look.
First, I cut all of the pages out of a hardcover book with an exacto knife, being very careful not to puncture the cover.
After this was done, I found a cute, floral fabric and used modge podge to attach it to the then-ugly hardcover. I did so in three parts, I cut separate pieces for each cover and the spine.
When securing the edges of the fabric to the inside of the empty cover, I used hot glue. Simple as that.
Once all of the modge podge was dry, I attached decorations. Mine were the owl and a silver ribbon.
For the side pieces, I just measured them to fit. I hot glued the edges down, then went back with my hot glue gun and touched up the parts that were visible, to make it look like more of a seam. I also hemmed it with the hot glue, but this was before I forgot to hem the fabric before I attached it as the sides. (My fabric was the same owl fabric that my big guy came from)
The strap was also glued in. I glued it to the sides, and I made sure to put the glue on a full two inches of my ribbon strap, and after they were both glued in, I glued in other pieces of ribbon over them to reinforce them.