I just got my Angie-approved luxe AT poncho--LOVE! Very fluid. Didn't stump-ify or overwhelm me at all. Lovely fabric. Wrinkles steamed out easily.
But what a simple design. My size ex/s is about 29 inches long by 25 inches wide. The way you'd make it is to fold 50 inches of fabric that has finished raw edges. The fold is your shoulder seam for your non-dominant arm. The top is left open from the fold for 12 inches, for your head, and the balance is seamed. That's it. It is a slight rectangle, with finished edges and a single seam.