Re: Shed foundation options
It bares mentioning that sheds are considered temporary structures which do not require permits. Temporary structures do not have permanent foundations, meaning no slab. That is not to say that you can't put a shed on a slab, but when you do you may be required to get it permitted and inspected.
Having said that, the most common practice is cement blocks to elevate the shed and pressure treated skids. As has been said, you want good air flow under the shed as this will help to minimize moisture/rot issues as well as discourage rats and other critters from nesting under it.
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