Here's a place to start, do a search for "hexagon warre beehives" and you'll find exactly where I started. Find the link that says "Beekeeping with the Warre Hive -- Hexagonal hive"
If you follow the links there you'll actually even find a calculator for your miter angles, but Drew is right, 30 degrees. Well the total angle at each junction is 60 degrees, but if you're doing mitered cuts, set your miter angle at 30 degrees. I had to set mine to 60 degrees, because in my design I joined the edges to the side instead of edge to edge..I hope that makes sense.
The volume in my hive is about 80% of a normal Warre hive. I originally designed it so that I could put a regular Warre roof on top. I did and hated the way it looked so I put the six sided pyramid on top and I think it looks much better. Have fun!