I am thinking you want it to look as much like a keyboard as possible?
Just took a quick look at my piano and since you are a beginner here's how I suggest you do it:
1 inch strips of fabric black and white. About 4" long.
Sew wbwbwwbwbwbw and repeat until the length is long enough. THEN add a 2 inch strip of ivory along the edge of border.
You can topstitch/quilt the piano key lines on when you quilt the project.
I would make the piano key borders exactly the size of the wall hanging and use corner stones in the corners as I did here:
http://www.quiltingboard.com/t-39728-1.htm It will make the project easier to finish.