I LOVE this fabric! I've got some on order from the USA at the moment and cant wait to get my hands on it! (oh hurry up mr postman!)
Easiest skirt pattern is:
1.5 x waist
Then length that you want plus about 3 inches (for the casing for the elastic and the hem - depending on what size you want them)
2 fat quarters should do it (did you say you wanted knee length?)
I didn't realize that there were any free Oliver + s patterns - I love them ... Off to look now