Amy's blanket was done in squares. Each person did a square of their own choosing and then several people got together to seam it.
There was no pattern, but it's easy enough to do. Just choose a size square you want (Amy's were 12 in squares) and make however many you want. Many patterns are not technically reversible in that the pattern won't look the same on both sides. Up to you how you want to handle that. Then you can seam them as is or crochet around the edge with a contrasting color. The crochet edge can be seamed more easily in many cases.
If you have trouble finding patterns for squares you can get a book that has a bunch in it. There are lots of them, but here are a few. I don't have them so I don't know much about them, but they seem to have good reviews. Try your library, too.