So I've found some information on the plans of the Zig Zag. There are a couple floating around the internet, but I've decided on one. There are LOADS of Zig Zag chairs that people have reproduced, and very few of them seem to be identical. Most have a 90 degree seat back (easier to build), or they are slightly taller, or wider than the original.
Since Cassina has been making the Zig Zag since the early 70's, I figured their design would be the most accurate. When you look at other Zig Zag reproductions, nothing looks quite as right as the Cassina. Since I live in the San Francisco area, I have the ability to actually go and see one of these at the Cassina retailer here. It helps a lot to actually get a hands on look at the design before building one!