Can't help with plans/details. For waterproofness, the yurt cover absolutely needs to drape down the outside BELOW the interior floor height. Speaking from personal experience I would either make the platform the size of the yurt, (so the cover extends down the outside of the platform) or much wider than the yurt. Why? If wider then you need to set the yurt on a platform built atop the larger platform, so the cover extends down as above. If you opt for the two platform system, simply make the lower platform that is your yurt diameter from 2x4 or 2x6 framed edge up. Insulate the bays with foam. The decking below will protect it from critters getting into it. Nice dry warm draft freefloor and no bugs. Have fun and good luck. Also remember if you opt for double deck system to leave gaps between the deck board on the bigger platform so water can drain off.