I don't have a good answer for you but I completely support the idea of reciprocal roofs. Would it have a skylight in the center?
Tony Wrench has some videos on youtube of them that I'm guessing you've seen. If not, or in addition, here's an ebook on building roundhouses with reciprocal roofs:
Tony Wrench ebook
Would the 6 support posts be at the center or midway up every other beam?
I'm pretty sure diameter is only limited by the materials you use, slope/design and your skill at assembling them. So 33' diameter (or radius

) should be possible.