There are far more experienced yurt builders here than I am, I'm just making my first one. You can read my thread here:
http://www.yurtforum.com/forums/buil...ublic-645.html
Plywood (2 rings, with spacers between them to form the rafter pockets) are described in the "Khama Yaminary"
, that are often quoted here. I'm sure someone will post a link to it soon.
The traditional crown has a strong symbolic meaning for the Mongolians, so they stick with the desing. If you want, you can use all kinds of materials and designs to make your yurt ring, incuding all-metal. Also depends on wheteher or not are you planning to use the baganas (ring supporting stands). If you're surely going to use them, you can get away with much lazier ring designs, as it won't really carry much weight.
My yurt is still not livable yet (I was delayed by flaws in the roof cover, just being solved by now). I'll be
it with a cast-iron woodstove (army surplus from the 50's), plus a spark-catching box next to it, which will help to keep the heat in as well. My yurt diameter is 6m.
p.s. that thing the Indians used is called ozan (at least in some languages) and it was a triangle piece of tarp that served as sort of auxiliary inner roof that helped to stop rain drops that found their way through the smoke hole. What helped them a lot to get the smoke out was lining along the tipi wall. It was a long piece of cloth that was tied to the poles in about eye-height and what it did was it left an air pocket between the outer wall and itself. This not only helped to insulate the tent, but as fresh air was getting inside under the outer wall (sometimes they left a piece tucked up to improve this), it hit the lining and was deflected up. This air stream took the smoke with it. Also different air temperatures came into play I'm sure.