When i lived in Japan for a year I couldn’t help but play these instruments and was sadden when I had to leave. Although I could buy one I would take much more pride in making one. I’ve decided to use hard maple wood for its properties in durability and ease to shape. Problem is I don’t have any dimensions to go off and after going through countless books and different sites. I am curious if someone may have came across some measurements or can offer insight from one that they made.
Hello Kevin
welcome to the community.
You might take a look to Kyle Abbotts awesome book ‘Shamisen of Japan’
http://bachido.com/products/shamisen-of-japan
It helped me getting started to play and also in building a shamisen, although only in 3D 
The book provides measurements, templates, step by step instructions and much more from beginning to finish and beyond. Check it out!
Cheers
Ale