I also made a rag rug. I used 7/32-inch nylon clothes line and my trusty Janome Memory Craft 3000. I wrapped 1" strips of fabric around the clothes line using washable glue sticks to secure the fabric. I then coiled the line in an oval shape and zig zag stitched the rope together. There were problems with the zig zag stitch occasionally that looked like it may be due
to the machine's bobbin tension. I remedied this problem by rethreading both the needle and the bobbin. Also a heavy jeans needle is a must if you try this. Here's a link to a tutorial that gives more tips. The blocking tips are helpful because the rug does not finish perfectly flat. You can get it flat with a bit of coaxing though.
The rug is very scrappy, purposely. I like the mixture of brights with low intensity colors. I find the muted colors break up the intensity of the loud bright patches and make the scrappy look visually pleasant.
As you can tell, our critters liked the rug. They were on it almost as soon as it was on the floor.