Jan, I think I got it from Thru-hiker just before they phased it out. I completed the bivy. I took the dimensions from SMD's Meteor, using the floor pattern for both bottom and top. The top was about four inches wider than the bottom, but I could have made the top and bottom the same, using the bigger top dimensions, as Mark and Dave suggested. Instead of curving the bottom ends, however, I just cut them straight across and added an oval-shaped end piece or foot-box 22" across 8" high to fill in the opening. To start, I sewed the two pieces, top and bottom, together all the way around except across the foot. Then, 13" down from the top I cut a the upper fabric straight across starting and stopping 3" from each side, then another slit straight down (from top to bottom) 22" down, 3" from the edge. This left a L-shaped cut. I put in one zipper going across and another zipper going down. When both zippers are closed, the zipper pulls meet at the right angle of the L. Note that the zippers are not in the seams, but 3" from the sides. I can have the bivy closed like a sleeping bag with the opening across the top opened or all the way shut if I want to hide. I have two zipper heads across the top opening, so that I could have it only opened in the center, or in whatever position I wanted to leave open a breathing hole. It weighs 7 oz. without seam seal, not yet added. I used water proof zippers, so I do not have zipper flaps. To add mosquito netting I would attach it to a zipper flap over the top zipper, so it could be rolled up there when not in use. To attach the lower end of netting I would either use a small zipper or velcro.
For the top I used Momentum90 from Thru-Hiker. Read about it at Mountain Laurel Designs under "Frabric Mojo". Water beads right off it, yet it is breathable. I chose red (crimson). It looks nice with the black bottom of silnylon.
Modeled the bivy on the deigns of the ID South Col
Pictures of my bivy here: