One helpful way to sculpt lip roll is to use soft mods and clusters.
Basically i started with one soft mod for a larger area (just clicked on center area of upper or lower lip) then i adjusted pivot and rotated soft mod to begin making lip roll shape. It wasnt a big deal whether it was affecting too large of an area because later i used a default blendshape to put at default areas away from lip roll.
Here's a picture of the process i was using on a amazing character designed by Alan Stewart (artofalan dot com).
Nate
