I Totally agree with Ed, (On all counts of his comment.)Over a half acre, might be worth it when you don't know where things will land. When you dig footers, rip it up a little but floor area will be set, solid. Pita for the dig, with having your rod guy with a razer knife in the ditch all day, but, big picture, still a win, imo. If you have a rough lay of the land, mebbe leave out some areas you know will be built on.
On a separate note, I wanna half acre spot for all my crap!!
But I digress.
You won't regret it, in the grand scheme of things.