Good question. Like Adrian, I limit continuous slope greens to a few, really 1 to 2 each course if I can. Greens that slope to the front right or left corner are reserved for uphill approach shots, where even the tiniest ridge would blind a lot of the green. On about half my courses I have done a Redan and/or the old Ross reverse slope green (typified by 12 (I think) at White Bear Yacht Club and 14 at Oakland Hills.
Using a digital level, and some advice from Pete Dye, I cap my continuous slope greens at 2.25% which at green speeds of 10 or so is on the edge of comfortable and scary, but doable. If I had any thought they would get greens to 13 or whatever, I would only go slightly over 2%.
And like Adrian, I also try to do some flattish greens, basically all 1.5% (minimum drainage for me). I can't really prove the theory works, but figure if I mix basic slopes from 1.5 to 1.75, to 2, to 2.25% it may confuse putters all day that they can never get a read by osmosis where every green has 2% slope. I like to think it makes a difference, but who knows?
As to shelves, at an ASGCA meeting one time, Jack Nicklaus mentioned he would never aim at a shelf target unless it was at least 40 foot diameter. That was good enough for me to make that the minimum size, and frankly usually go 45-50 feet to allow for the edge of the green creeping in.