I'm hoping you guys can help me out on this one. I have a customer who wants a mortared flagstone patio about 750ft2. The difficult part is he has three doors on the back side of the house about 18" off the ground. He does not want a deck since we are pulling the old one out. Does not want pavers either. We are considering a split level patio with a 7" drop off of two of the doors leaving about an 10-11" slab to be poured. Is a slab that thick likely to crack? Do we need rebar? I'm concerned about settling issues and think we would still need a 4" abc base minimum. Any thoughts?