Thanks for the reply! After drawing out my plans, and drawing up a CAD of the dome, I don't want to get in trouble with the city, so I am rethinking the height of my building. The good news for me is that my job is much easier now. What I plan to do is to build a deck within the dome, and put a 5/8th on 4 foot posts. (This is all based on my calculation of 5/8ths of the diameter of the sphere being: (((5/

*20) + 4 = 16.5' ).This way, even if it isn't level, I can straw bale underneath it, I don't have to tie in each post to another inner ring, and I don't have to make all the complicated cuts which would have been involved with that. So I will be building a 6 foot deck as a perfect square inside the dome. This way it will be protected immediately from the elements as well, so I don't have to save up to build walls on the outside.
What would be the best sheathing for this

I figure for now, I will put clear polycarbonate on the uppermost section of triangles, and to save money, put white vinyl on the lower portion of the dome, with some windows I will fabricate from acrylic. What else do people do with conduit? I was thinking double sided tape to secure the vinyl, and then waterproof UV protected tape (like Eternabond for RV's, but the cheaper version) on the seams to waterproof it. I am aware that I will have to pull this all down in a few years when it decays from UV exposure, but hopefully by then we can afford the polycarbonate all around the dome. The tape will be the most expensive by far, but I found an acceptable price for it online. I can hang a wooden 1x2 window from the conduit without putting much stress on the structure, and I will put about 4 of them at the top, and 4 at the bottom. I will just use 4" duct in the knee walls, to bring in air, and eventually build a cupola with a permanent square vent at the top, to pull some cfm's, creating a vortex around my inner deck, and keeping it cool. These vents will be pre-warmed for the colder months by my rocket mass piping, which will run around the perimeter of the wall.
Any suggestion on the fan size (and dimensions if you would happen to know them) for a 20 foot dome sitting on a 4 foot post? Also how would one frame out a door for a dome like this. I am going 4 feet down, and I am sure this would be strong enough for a door, and even a patio door, without any support at the top. The only puzzle I have with this is how to tie the conduit into the door?
Thanks again for the reply, I have found some useful stuff on the links!