Some of the common sense aspect of this design:
The outer cover is about 6 inches above ground, the inner liner goes from the ground to about 6 feet. It is fastened to the inside of the poles. This creates a 6" wall cavity, cool air is sucked in from below and spills out above, this creates a draft so one can have a fire inside and the smoke will draft out the top. Any rain that would come in thru the top runs down the poles in the wall caavity, down to the outside, keeping the inside dry.