I'm leaning toward the 1.6 PU4000 for material. The roughed-in dimensions put the base around 13' x 13' and I need to decide on height. I use Sketchup for design, then will comp a scale model or two.
I'm really not too concerned about the final weight. I'm using it to shelter a minimum of 3 guys +gear, and a maximum of my wife and me +3 boys. Almost any other option is going to add up to more weight, and I'll hoss a few extra pounds to provide the experience a tipi brings to the backcountry.
My initial design could be crazy, but it factors in using the max width of the fabric roll, then I'll divide a length of roll into two triangles. This ends up with a 10-sided tent with very little wasted material.
I just picked up a couple huge projects, so I'm slammed through the end of May. I'll try to work in the design before then so I can get it posted for feedback.