If you have a large carpenter's square, hold your arms up as if you are shooting a gun and have someone hold that framing square in the pocket of your shoulder where the butt of the gun would sit, with one leg pointed down to the floor and the other out in front of you, roughly mimicing the position of a rifle. If you are shaped like most people you will see that the square does not point out level relative to the ground, rather it points slightly down toward it. That angle is what you would want to mirror in the pitch of the butt. Usually that means that the toe of the stock is slightly longer than the heel. You are only talking a few degrees. Too much pitch and the stock will try to slide down the shoulder under recoil.
Lots of factory guns have neutral pitch, so that certainly works. But a little pitch is a little mo gooder.
