Is a floating perimeter slab a good approach for a dirt-floor shed?
Yes, the poured, floated &amp; sealed afterward slab is the best way to go, if you're up to it, &amp; it's the best anchor. Definitely do at least a 4-inch bed of gravel under everything, this is what moves instead of a slab or blocks or pads.

However, absolutely consult your Building Dept. first &amp; foremost. They have plans for their requirements &amp; you'll need a permit &amp; likely 3 inspections. They have to approve your plan &amp; that approval will hinge on if you can do anymore "paving" on the property, if the shed/coop placement meets setbacks &amp; if the planned structure is sound or even big enough for your vision.

Other than that stuff, going with blocks filled with concrete is pretty solid &amp; much easier. If anchoring the building is done like putting in fence posts then just concrete pads halfway in &amp; halfway out around the perimeter would accomplish the same overall desire &amp; be the easiest by far.

Oh I initially forgot, if the back, friend &amp; truck's good you can possibly use parking lot Wheel Stops (6x6's) for the foundation or more. There shouldn't be any monolithic requirement &amp; they're higher density concrete that's rebarred. It's slightly rednecky, but saves an awful lot of bag hauling, temporary lung damage, form work &amp; drying time...you'll love the pinning holes too.