I always cringe when I see people roll their shoulders. It's the same reason why you shouldn't do lat pulldowns behind the neck...you're straining things. Straight up and down, bro.
Rolling your shoulders puts undue stress on your rotator cuff and does zip for any added muscle growth. As previous posts tell ya- stick with just straight up and down. To spice up your trap workout try this- Go to the standing calf-machine at your gym and use it for shrugs. It helps take the stress off of your grip and allows you to concentrate solely on your traps.
I think we have an agreement that rolling be no good...
I like to start the rep with my shoulders lowered as low as I can droop them.
Then bring them straight up or a little to the rear, hold for 2, then slowly let them down, not dropping them.