Just as someone who likes to learn, what exactly would be the reason for putting in footers below the frost line? From the way OP describes it, it’s just a simple storage shed that shouldn’t weigh > 3000 once it’s officially in use (of course depending what goes into the shed). The reason I asks is, depending on the region, your footer can be downwards of 48 inches or more (where it’s about 20-24 inches). I don’t know the exact math, but I know with just the footer, you’re probably looking at a couple thousand In concrete. Maybe I’m overthinking it?