Of course there were many questions in the comments about how???? Jamie was very sharing and gave the website address for the directions and also mentioned that it could be fashioned smaller using a half a sheet. It would be approximately 5 x 7 inches. Now, that's my favorite working size. I must do this!
Here is the link Jamie gave:
This is my 5 x 7 adaptation and below I've provided directions on making a basic book. The sky is the limit for what you do with it :)
Please click to enlarge images. This book has 16 paintable surfaces.
You'll want to use Fabriano 140# watercolor paper as it doesn't crack when folded. I tore my sheets so I could get an uneven edge. I use hot press as I like writing on the smooth surface.
Your book will be as precise as your folds. Take your time and you'll be happy. I practiced on a 15" x 22" sheet of drawing paper. I'm glad I did!
Happy journal making!