If you're thinking of the classic uniform from the beginning of the series (when draco's so tiny and cute xD) then here's a full body picture of him: http://images.wikia.com/harrypotter/...oQuidditch.jpg
and this: http://4.bp.blogspot.com/_0uqYbd3bIA...oster__red.jpg
Here's a picture of just the costume itself: http://feltbeats.com/wp-content/uplo.../IMG_20281.JPG
Later on in the series, though, the quidditch uniforms turn more into thick wool sweaters and pants, but I was probably thinking this is what you were thinking of since it's more classic ;D I hope this helps a little~
My suggestions for a pattern is this: http://www.simplicity.com/p-2272-mis...-costumes.aspx
You could use pattern B, sew it as instructed; then, you could shorten it to the length you want (about to the thigh), cut the fabric off 5/8" below where you want the robe to sit on you, then fold up the fabric 5/8" on the inside, press it, and then sew the new hem in place. Also, you would then have to add holes in the torso to loop the threading through. Your sewing machine most likely has a button-hole maker, and the instructions on how to work yours will be in the machine manual. You could use that and make the appropriate holes. Or you could use one of those thingymagigs that you can buy in fabric stores (GOD I NEVER LEARNED THE NAME OF THIS XDD), the little gadget that punches metal hole linings into the fabric; this will probaby be easier than making button holes and would look alot more authentic.