I still remember how excited I was when I first learned to do a flip on my quadcopter! I managed to get it right with the cost of breaking a couple of booms and many many props, but it's all worth it.
For example this is how I do a flip, same applies to roll:
- Generally you punch the throttle to get some upward acceleration
- Reduce throttle a little and give hard roll (push roll stick all the way to the end in whichever direction)...
- Once the quad has turn NEARLY complete the flip (360 degree), recover roll stick position and throttle up again to recover
Do it over tall grass the first few times
I suggest doing it in LOS first, once you mastered the sequence of sticks changes, then move on to FPV and it gets easier.
Here is a video of Flitetest demonstrating how to do it... pretty useful: