A couple things that I have learned over the years... When Adjusting your handlebar roll, keep your fingers off the brake levers! I see a lot of people reach for their brake levers when adjusting their bars which will rotate your wrist and may throw off the perfect roll for you. Bars first, then brakes. Also make sure your actually standing on the bike and in attack position when trying to find that sweet spot, so many people do it when sitting down on the saddle or just standing on the ground, this makes a huge difference! As for brake...
To help make sure your bars are properly lined up with the fork, put a straight edge or ruler of some kind across the fork stancions. You now have a larger reference point on which to adjust your stem and get your bars straight.