It makes a great cover.
If you size up one size (so that you'll have enough rise and width to cover the diaper) and use the INSIDE pattern peice (sounds weird, but since you won't be turning the seam allowance to the inside, it works well) for the SIDE closing diaper (even if you want a front clsoing cover, use the side closing pattern piece because it already has the lower rise since you don't fold and tuck like on the front closing one and it's already rounded). Extend the wing ends a half to three quarters of an inch and make them rounded. Bind in foldover elastic stretching where you would normally put elastic and not where you wouldn't. With one layer of PUL, these amke some of the softest and trimmest covers we've ever used! Love side aplix covers.
Seriously give it a try. If you are using a large diaper and need a cover, just increase the rise of the large by an inch and you'll be good to go,