I used corrugated garter in an acute triangle shape finishing off with the i-cord. Originally, I didn't have the i-cord, but my mom and I discussed and decided that I really needed more to the shawl.
I used fingering weight and light fingering weight yarns blended together so I think yarn in either of those weights will work. I do recommend that you swatch with your colors in the corrugated garter first to make sure that they will actually show up.
In Dillon I used the same garter stitch technique and I picked colors that were much too close together so you couldn't even tell I was using two yarns! If you are going to put some work into knitting this shawl you actually want the colors to show. So swatching is more important in this shawl than my usual designs.
Happy Knitting! Sierra