Under it is rocky soil.  

But I think the issue with that property is actually the soil it was built on. 

They probably didn't do the final finish sand.  Is

You typically want to make sure the land is suitable to support the type and size of structure proposed, so you want to get some soil test borings performed by a local geotechical engineer. 

The environment we grew up in is the soil. 

My well is bringing up very sandy water so I had a fancy (read expensive) sand filter installed.

If there is at least 2-3 ft of soil below the current slab and the foundation, we would only need to excavate, place new insulation and gravel then a new slab.

My socks felt soiled when I left, from walking the house.

So you need to figure out type of system.What are the soils like? 

I have been looking primarily in the Buckhead, Brookhaven, Sandy Springs, and Vinings areas so far but can be persuaded to look elsewhere based on any recommendations in this thread.