foundation for a hot tub?

You didn't give any details but all you do is turn down the edge of the slab to create the footings. We just use a 5-6" floating slab with 6x6 10ga wwm but it really depends on how much weight is placed on it, where you are located (frost), and what the soils are like in your area.
The best advice is to just call the local building dept. they'll let you know what's needed for your area or ask any local H-tub supplier.