There are guides on sites like x360a.org, but I found it hard to keep my minions alive so I just stayed behind Rollie. Take a few swipes, and move to stay behind Rollie. It takes a while, but it's pretty simple. At 50% health, he will occassionally charge but if you're behind him he'll just run into a wall and stop. Swipe away. You should be able to shave about 10-15% of his health off each time before he starts turning.