There are a few books available on Japanese timberframing, but the only one of much use to you is the translation of the Nakahara book, "Japanese Joinery" (Hartey and Marks, pub). It has a limited section on Japanese roof framing as well as the Japanese method of doing Western (German, I think) truss roof framing. If you are experienced at roof framing and are really keen, you may be able to derive enough info from this book to build a basic Japanese roof. Otherwise, you are going to have to get some help, particularly if you are interested in an uplift at the roof edge w. curved hip rafters and the rest. There are many books available in Japanese on the intricacies of roof layout, but if you don't read Japanese you are going to have a next-to-impossible time trying to decipher it.
There are few people in N. America familiar with real Japanese roof construction, and only a few companies that do authentic work in this regard that I'm aware of. You can try Eastwind Inc, Joinery Structures, of Horiguchi-san, all based in N. California. There are two Japanese carpenters in Washington state as well. I am based in B.C, Canada, and I could be of assistance to you if you are stuck with something in particular. I lived in Japan and studied timberframing there, and brought back several roofing texts with me. Even though i read Japanese, it requires a LOT of work to figure out what the heck is going on in some of the schematics, and I've been studying the use of their framing square for the past 2 years (with no end in sight!).
Keep in mind that the Jpanese roof does not stand alone but needs to be totally integrated into the design of the wall framing, particularly in regards to the layout of the plate.
I hope this helps you out. Good luck!