* it may not raise property value, a twenty foot green house decreases the value of the property, to raise value it has to look like something “normal“ as TV/ toilet/ or at least plumbing roughed in for a half bath and kitchenette.
* you are basically describing a walk in basement so the cost shouldn’t be too bad. It would be functional with a patio you can drive to and to look “normal”, when selling I would stage it with a fire pit and seating. The door should be a double wide to make it easy for equipment or the next owner to put in French doors for a party area.
* floor drainage sloped to a drain, I hated the spots in the pilot plant that caught water.
* you are talking about some interesting wine volume with floating lid tanks. I would do at least ten foot ceiling height, possibly twelve. Plus,, Your extra ceiling height is basically free volume.
* benches? maybe stainless tables with wheels, flexibility is valuable, and you can roll them outside when the vinters club invades.
* I would look at a flat deck for the roof, it will add cost but changes this to another party room in the eye of a buyer. A steel truss with poured concrete floor is common construction.
* steel trusses were good for hanging unistrut and mounting equipment without calling a contractor.
* if you have a concrete roof/ ceiling consider building a penetration for the future as venting heat, or pipes and wires, or a pipe from a crusher set up, or another half bath, etc. etc.
