One of the fastest way I have seen to build relatively inexpensive mining industry shop buildings is concrete tilt up.
The first one I saw done was about year 1970 near Paintsville KY and that tilt up building is still used as a warehouse today.
This video shows the kinda “deluxe version”
but the basic concept should be clear:
pour the floor,
then use that floor as the lower side of additional concrete forms that create the other building walls and roof.
https://www.youtube.com/watch?v=kC_pEaccZQAThese buildings are investments that an prominent thought to hold in mind is: what can I sell it for in the future?
