As far as effect on rolling is concerned, it depends on where the thermal is. If you are rolling left and the thermal centre is to your left, it will tend to roll you wings level, if it is to your right , it will tend to make you roll further than anticipated,and depending on the strength of the thermal and your closeness to its centre, the effect can be very pronounced, alarmingly so if you arent used to it.
It is not uncommon for early solo glider pilots to land back on thermic days saying that they couldnt find a thermal because unless they fly into it more or less straight through the centre the lift lifts one wing and effectively turns them away from it. If its subtle they dont associate it with nearby lift.
Towns and large areas of tarmac/concrete tend to be good thermal generators and brown fields are better than cropped fields. How the land drains has an effect as does slope - south facing warming up quickly.
All that free energy out there - use it if you can!