The pattern states that Ruffled Roses finishes at about 90" x 90", so you need an assembled binding strip that is about 372" long.
(That is 90" x 4 sides + about 10" for the corner folds and final joining.)
370" divided by 42" (width of fabric) means you need to cut at least 8.80 strips, so bump that number up to 9 strips.
Add another strip to allow for piecing all the strips together, so you will need to cut 10 strips of binding fabric.
(Page 2 in this tutorial shows how I join my strips together:
http://www.thequiltshow.com/os/images/lessons/5/1095/1095_2011_tqs_bom_3_mini_piping.pdf )
If you need to cut 10 strips of binding fabric at 2-1/4", you will need 22.5" of (42" wide) fabric.
Be sure to allow for squaring up the fabric before you cut it.
If I were to purchase new fabric, I would ask for at least 2/3 yard.
Well...actually, I would buy a whole yard....but that's another topic!
Did I ever tell you that I love scrappy quilts??