Pete, I cannot for the life of me figure out how somebody swims with a roll. Do you mean double back in a circular fashion? Turn from one side to the other? What is a rolling-style of swimming????
Mmmm, how do I describe it, Essentially with a slow but slightly bold flutter kicking style let the force of a kick roll your body one way so you body, face and view shifts to a side. The next and opposite kick passes your through dead center and sweeps the view to the other side. It's sometimes referred to as "screwing the water". It's not a 180 roll but gives a more panoramic view of the area.
Pete