Take note: I wove these samples on the end of a black-and-white warp that was left over from another project. Really, I was just curious about how to weave curving pleats. No way would I use black and white yarns if I were weaving this for a garment!
Anyhow, I'll get to the point. As we all know from that inspiring book, Fabrics That Go Bump, when you weave a turned twill on 8 shafts or more, you can create vertical pleats. The secret lies mainly in the structure, which is basically a turned twill that alternates between weft-emphasis and warp-emphasis blocks.
Here's a look at a design from this book by the late, great Erica de Ruiter. I found it inspiring.