I'm pretty much self-taught due to my location (not many kayakers around where we live). I've found the Qajaq Rolls / Rolling with Sticks website fantastic! Lots of great videos of practically every Greenland roll and it's all free although I did buy the dvd and workbook. I also purchased This is the Roll dvd which is also great.

http://qajaqrolls.com/2013/12/getting-your-first-roll.html

Christopher is a great guy, mentor, roller and is always willing to answer any questions. 

Good luck!

Tony