You'll need to clear out the area and add concrete or another material, then build a wooden base. If you're going to use your shed for something like storing firewood, pallets could be used for ...
Let's be more creative, and use a Slime Incubator to fill their Shed with 'em instead. Another great option is to just forego the Slime Hutch entirely—build a slime Shed! Given the substantially ...