My contractor just poured a 17' X 17' slab for my enclosed patio. It has a 3.5" step over the sliding door into the back yard. I think that the slab should have been built higher so that you dont have to step over it to get to the outside. It seems like it could be a safty issue. should he put in a subfloor so that the transition from the inside to the outside is even? If he puts in a subfloor, it would be a 3.5" step down into the backyard. Which makes more sence to me.