We did an Ostrich round robin a few years ago in my guild. It is the same as your “roost” as an ostrich doesn’t fly.
Each round we gave participants two options. For example, use a different shade of one of your previous colors- lighter or darker, or add applique. One time it was use a new to you piecing technique.
I just watched Winnie Fleming’s Craftsy class on borders and I wish I had this information when I did a round robin before. No affiliation, I just found it very helpful.
http://www.craftsy.com/class/finishi...bb&_ctp=4813,3