Raised Patio on a existing concrete slab

[jmkr02]

Customer called wants a 6-8" raised patio over the existing concrete pad. I need to meet the customer and see what they are looking at doing. "Other "experts" say good to go, but the concept to me makes me cringe. I say there is a chance of drainage issues, void space under slab... freeze thaw issues...

I guess the base from a compressive stand point would be strong, but a raised paver patio is more permeable then the concrete.

Then there is the intrest in using a wall block either on the slab ori around the perimeter.

Arguments Please!