Here's the instructions I used when I learned how to make a rag quilt. I have made them using flannel, denims, and fleece. And I make my squares as big as I want to, so don't feel locked into doing 5" squares, I do 8" and even 11" squares, and they can be one ply or two. I do a lot of fleece with only 1 ply. And on the flannel rag quilt, I don't always include a center piece. It depends on where it's going. I live in So. CA, a 3 ply blanket is just too warm here, and it can get pretty heavy too if the blanket is big enough. And sometimes the directions recommend using a walking foot but I just use my regular machine foot. I guess if you are doing a thick rag quilt, with 3 plies, a walking foot would be a good idea.
Hope all this info helps.
http://www.lovetosew.com/makeragquilt.htm