I make my pads from 6" x 5/4" decking cut to 12" lengths. My focus is to make for a larger area to help distribute the coach weight and prevent damaging the campsite. I think I've used them maybe three or four times over the past ten camping seasons. Most of my travels been state and federal camp grounds the gravel sites that have all been hard packed from many years of usage and not needing landing pads. Had one one stay at a commercial CG that required landing pads.
Wood pads cost me about $15 for a set of four cut from a 16' decking board.