My understanding is that a full roller is when your initial ball track runs around the ball between the finger and thumb holes, basically cutting the ball in half.  A leveraged full-roller will usually start to roll early and fairly strong on the lane.  It was a popular drilling years ago, but is not popular now.  The risk of this drilling is that you may roll the ball over the finger or thumb holes, which will usually diminish the striking power of the shot, especially if you are hooking into the pocket.  There are some variations to drillings for full rollers which a certified driller can offer to you depending on how you throw the ball, what you are throwing and where you are throwing it.
I have had 3-3/8x3-3/8 full-roller 7:30 drillings on equipment in the past and that worked pretty well for me on medium-heavy oil, even though I actually have what is called an "inverted" high track.  

Some others here may give you a little more info and advice about this issue.
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"Chopping Wood For over Two Decades"

A 7:30 (full roller) layout, reverses the flare of the ball. The flare rings go counter clockwise (away from the fingers and towards the thumb). Doing this on a normal 3/4 roll bowler will cause the ball to roll over the thumb. But, this is also a very early rolling drilling and can work wonders on lot's of oil, when nothing else will hook/hit. =:^D