Let's say it's walled and roofed, however it just sits on a concrete slab...not anchored in any way...such as a "doghouse" over a well/pump...I don't believe that would be considered a structure...so wouldn't it, in addition to being walled and roofed, need to be "tied-down" to the foundation in some sort of way...whether it's by sunken posts or straps or something to actually anchor it?
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My opinion only. Not legal advice.
Say you'll haunt me - Stone Sour