Simply Differently has a good calculator for determining how to sew up a yurt canvas, with very informative illustrations.
I made my first layer of roof
in the pieslice-wise method--it was a bit of work cutting out all the slices, hemming them, & sewing them together. It made a lot more seams than just a plain lane-wise setup would have...
For durability, a sacrificial top layer is a good idea. Something not too heavy (ie, not a pain to work with like thick canvas) or expensive, since it'll require replacing every few years. But it'd keep your expensive water-proof canvas protected from the sun, potentially extending it's lifetime from 2-3 years up to 5-10 or more.