If I look at the above-mentioned Google search, there are also numerous pages
e.g. the one from holzprofi24
"Whether a foundation is necessary and which one is right for your garden house depends on its construction, the condition of the soil, and the purpose of the building, which may require a water or electrical connection."
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[*]Small tool sheds can basically also be built on compacted earth. However, especially in loose soil, it is advisable to use a layer of compacted gravel or sand as a base. This provides support and helps with drainage after rainfall.
[*]Lightweight garden houses with post-and-beam construction can be founded using so-called drive-in sleeves. The metal sleeves are driven into the earth with the help of a sledgehammer, after which the posts of the tool shed are anchored in them.
[*]Larger and heavier garden houses always require a foundation to compensate for ground movements. Different types of foundations are available for the various building types.
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So if that’s not what you’re looking for.
There are certainly quite a few other pages there with further information.
If you say how big your garden house should be and in which construction style, then one or the other here might be able to help you sort it out.