I made one for use on the AT last summer, it was a perfect match for my MLD poncho tarp, i made a couple of tweeks on it like a mesh opening for the footbox which is nice on the hot nights. i also added a skirt of silnylon around the perimeter of the bug netting (thats connected to the zipper) to enchance the splash factor and wind ristance some. i highly enjoyed the mesh opening for the foot, because i could vent the bivy further and cool off me feet. but if it was rainy out i could cinch it shut to help with spindrift. for materials i used nanosee-um netting, silnylon bottom and momentum top. i'll try to get you some weights, but im still waiting for my new scale... once you make a paper cut out, its fairly easy to make.
let me know if i can help ya out,
p.s. for the record this should probably be under the make your own gear forum, but no biggie.