|I saw this type of sleeve on various RTW tops and I liked it, plus it makes a knit top even easier to sew, as it eliminates the sleeve seam.
How did I draft it? Took one of my knit tops patterns, folded the sleeve pattern along the shoulder mark on the sleeve cap. I marked on the bodice the seam allowances (the pattern is Butterick and therefore comes with seam allowances included) at the side seam and at the armhole seam. Similarly, I marked on the sleeve the side sleeve and the seam where the sleeve joins the body. See how I did here - http://www.flickr.com/photos/laura_lo/774454255. I then marked with a dot the two intersection points: the one between the armhole seam and the side seam on the bodice and the one between the side seam and the sleeve seam on the sleeve - see the red dots in the photo linked above.
Using pushpins, I then matched the seamline drawn on the bodice neckline (at the shoulder) with the sleeve seamline (at the shoulder mark) and then the two intersection points. See it here - http://www.flickr.com/photos/laura_lo/774454247/.
I then decided on the length of the sleeve and drew directly on the knit fabric, around the new pattern (treating sleeve and bodice as one piece). I checked with one of my RTW tops and it's exactly the same sleeve, so I must have been doing it right!