Costco Members: 8' x 12.5' Lifetime Resin Outdoor Storage Shed Expired

From the manual [syndigo.com]:

You must provide a platform on which to assemble your shed. Proper building permit documentation may be required in your neighborhood. Consult all local building codes prior to assembling the shed. Before beginning assembly, you must pour or construct a platform. There are two types:
• Concrete
• Wood Frame
Select the type, but know the surface must be leveled and flat before installation. If the surface is not properly leveled and flat, the shed will not assemble correctly. Proper surface leveling will save you time in the long run, so please do not ignore this step.
We recommend a Concrete platform. It will be the most durable and long-lasting choice. The platform you choose must be built above ground in order to avoid water pooling inside the shed. All lumber must be rated for outdoor use.
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From the listing on Costco:
https://content.syndigo.com/asset.../1920.webp
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From my experience, having set up dozens of these over the years for myself and others, the foundation must be flat. If you have thaw/freeze cycles, 4" (or more) of concrete is a very good idea. If you're in the southwest, you can probably get away with concrete pavers over a crushed rock, compressed, base layer.

If you are doing a smaller shed and not storing anything remotely heavy (e.g. bicycles, children toys, pool accessories, etc.), then you can get away with flat, hardened earth and just level it, or a paver/stone foundation.

But for something this size, particularly since it will be there for a while, I'd highly recommend a good foundation. The repeated stress of walking inside of it, or parking a lawn mower or other heavy item, can torque the resin components and the fasteners can sheer off or crack the connections. It is a great product but absolutely needs a good foundation based on use.