Storage Shed under deck

Hi everyone. I have a room off my kitchen that is built above an empty space, supported by steel beams. I'm looking to build an enclosed storage space 12'x12' - 6ft high ceiling space.

I don't want to pour a concrete slab for the floor and would rather leave it as crushed stone. Does anyone have recommendations for building/framing walls on this type of ground flooring? I live in New England and worry about frost heaving pushing and pulling during winter months. I would love recommendations to consider.

Thank you.