Here's a ridiculous amount of information. 90% of the knowledge I used to build
mine came from there.
The Recording Studio Design Forum
And here's the book that came out just after I finished, though Rod is one of the very knowledgeable contributors to the site above.
Rod Gervais' book, Home Recording Studio: Build It like the Pros
Good luck! You'll love it when it's done... but it's not an easy process.