I've made a poncho/tarp before, and I had problems from making the hood too big. So make sure you take your time when it comes to designing the hood portion. Mine constantly fell down over my eyes! Poor engineering on my part! One con that I'll mention about rain gear that doubles as your shelter is that you can only have one or the other. I like to be able to set up camp and wonder around without getting wet. Also, if you have to go relieve yourself in the middle of a stormy night, it's not such a tedious task when you have separate rain gear.

Eric