Any yarn with suggested hook will work: the size of finished rose will change depending on what you use. This pattern is for the rose portion of the Granny Rose Square, but the other portions can be found below:

1 of 5: Info and Supplies
3 of 5: The Leaves
4 of 5: Granny Edge and Joining Squares
5 of 5: Joining Sides, Edging and Buttons