I know you press c to crouch but how do you role?
Simply press the keys for movement to either side. You're probably using WASD keys, so A to roll left, and D to roll right while crouching. Note that you will have to press these keys while stationary. If you're moving forward while crouching, you'll just change direction, not roll. You may also be suing the Arrow keys, in which case, left arrow for left and right arrow for right. Happy Rolling!