I had to look back at your last post to discover that by CW you mean Cathedral Windows. (My first guess, Civil War, was incorrect.) Please look at this tutorial before buying the fabric, because she gives specific recommendations on selecting fabric and explains why. She also gives directions on calculating how much fabric, and your 11 yards estimate is pretty good.
http://hyena-in-petticoats.blogspot....-tutorial.html
I've never made a CW (now I'm using the abbreviation too!) quilt, but it's on my list. Good luck with yours!