Here is my poncho/shelter which I promised some time ago. When we first made this (back in 2000 – for my first ‘moose hunting’ trip to Supper Cove, Fiordland) there was no such thing as a waterproof zip. As you can see we used 2 oz ripstop and Velcro. Della made three of them in such a way that they two or three could be combined to make a bigger (and bigger) shelter by joining them edge to edge (which I still think is a good idea if you sometimes tramp with friends).
Now that there ARE waterproof zippers (eg here: http://www.zpacks.com/materials.shtml scroll down – 13 grams and US$4.78 per metre) you can make a far more waterproof poncho using (probably) 1.3 oz/yd2 ‘silnylon’ (eg from here: http://www.questoutfitters.com/coated.html#SILNYLON%201.1%20OZ%20RIPSTOP ) – US$10.49/yd = 2.5 needed) OR .51oz/yd2 cuben fibre from either of the above if you want it ultralight. (NB zpacks have .67 oz/yd2 cuben avail. In camo!) In silnylon it will weigh a little over 150 grams; in cuben it will weigh less than half that – about 65 grams! That is a SERIOUSLY lightweight raincoat AND tent! You would make the tie-outs out of Grosgrain ribbon (available from both of the above).
PS: You will see I have updated this to be a 185 gram tent: http://www.theultralighthiker.com/the-pocket-poncho-tent/
You can see how to wear it as a hooded/hoodless poncho in the pix, and how to pitch it as a shelter here: http://www.theultralighthiker.com/pitching-the-poncho-warning-this-may-save-your-life/