Definitely not sterling board for floor Dave. I know it's less expensive than ply & chipboard, but it's a nightmare to scrape. Not a problem on roof, providing you use enough joists to stop it bowing. Remember, if you have a roof problem, not a big deal to fix or even replace, but you can't do that with a floor. I always use 3/4" or 1" chipboard for floor, the only thing I do is when I have the floor built, is to give it 3 coats of creosote before laying it down. OMO.