I finally made my first "real" MYOG project, the reason I bought a sewing machine.
I used sil 2nds and ripstop from Quest, and my tweak to make this fit me was that I added 6". I'm 6' and about 180lbs, and I use a long bag, so the added length was necessary. I added it to the hood area, 3" to the mesh and 3" to the nylon hood; that way I still only used two yards of the top material.
I also made a side zip using one continuous zipper. It was a pain, but I think it was worth it. Rather than try to make the zipper do a 100 degree turn, I added a small triangle to the mesh, turning the zipper twice in smaller angles. It works quite well.
Hood end with my Sub Kilo and Z-lite.
Foot end. I also made the corners 10" high because I have size 14 feet.
Close up of the curve in the zipper. Someone with better sewing skills could've done much better.
Final weight: 6.7 oz without trimming the seam allowances. I haven't decided yet if I want to go back and add stitching to make them lay flat.
Thanks to Jamie for making the pattern, and thanks to everyone for posting their bivys. The discussion and pictures helped me a lot.