[lbrachfe]

Simply have your Newell weighed and contact a concrete company for the proper composition and PSI for your load and the proper depth and material for the sub base and as Tuga stated Prep is the key as it is in all construction. My guess from 35 years building is a sub base compacted to the freeze line or in warm climates 30". Use a minimum of 4500psi fiber laced concrete and 1/2 rebar boxed and wired in 24" pattern. Concrete depth depends on your natural base and fill, but no less than 6" depending on all other factors and score expansion joints in a pattern and more if you have a severe pitch. Good luck and you should be crack free....