if you can make a stuff sack you can make a drawcord bivy. Make the breathable part narrower than the coated part. sew the mesh to the breathable top, then sew the top to the coated bottom along the 2 sides. Sew the bottom like a square stuff sack, see thru-hiker.com. That should get it for you. you may want to seam seal the 2 vertical seams in the footbox on the coated fabric.