Because Gravity Falls is freaking awesome and I am a nerd, I decided to make my own 3 book the other day. 
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My brother really wanted to make one (he tried to use my moms first edition books from the bookshelf lol) but your's is awesome! I'll have to show him. ^^
Hahaha, tell him to go take a trip to the craft store and just get a sketchbook. That way he can fill in the inside as well.
your welcome!