The guy I subcontract for wants me to build a 20x15 on a sloping back yard. The back will be 15 feet high. I built decks before but they where under 4 feet high. I feel confident on the deck part but I'm not sure about the pilliars. I would like to stick with wood if possible. Im thinking 6x6 posts every 6 feet to 8 feet bracketed to cement pilliars. Then x braces 2 high. Is pilliars needed on the sides if my floor joists can span the whole distanceand does it have to be x braced? Is 2x4 strong enough for x bracing? what else can be done to stop wobbling? How high can make my cement pilliars if i cant get long enough 6x6's. Will 4x4's work? Is this project to big for a diy deck builder?