Technically, a snap roll does not use the ailerons. Its all done with elevator and rudder. Some pilots cheat the entry by using ailerons to induce the stall on the inside wing. Some planes will naturally snap without even using the rudder (e.g. CAP 232). The typically snap is done by pulliing (positive) or pushing (negative) the elevator and using the rudder in the desired direction of the snap. Calling it a roll is almost a misnomer, as its technically a spin, since it is a stalled wing maneuver. They can actually be performed pretty fast, but your plane better be built to take it. It puts a tremendous amount of stress on the wing.

Do a google search and you'll find lots of opinions.

Brad