Building A Light Duty Shed Foundation
If you plan on putting a light-duty shed on top of a
concrete foundation, there's no need for any footings and you might even
be able to get away without installing any structural reinforcement.
Here is an example of an extremely light duty shed foundation. Let's say that the shed is going to be 10' x 10' square, I would suggest that you make the concrete foundation at least 2 inches longer, just to make sure that the shed has plenty of room to rest on.
In other words make sure that you build the light-duty shed foundation at least 10 foot 2 inches, by 10 foot 2 inches square and you shouldn't have any problems installing your new shed on this concrete slab.
Now here's something that you need to consider, you could probably get away with a minimum slab thickness of 4 inches, if you have good soil conditions. If you're not sure, what your soil conditions are, it would suggest that you increase the shed foundation slab thickness to 6 inches.
If you would like to reinforce the light-duty shed foundation, you could install some 6 x 6 wire mesh. This is usually a common building material, used for concrete foundations and most lumberyards or building supply warehouses, should carry this product.
I don't recommend making the light-duty shed foundation any thicker than 6 inches. But if you would like to add some more structural support and really have a solid shed foundation, you can forget about the 6 x 6 wire mesh and install number 4 rebar, 16 inches on center, in both directions of the shed foundation.
In other words the rebar will crisscross each other, forming a grid like pattern. If you use the rebar, and the six-inch concrete foundation slab, you're going to have one heavy duty light-duty shed foundation.