Idea for cold cellar
A shed it’s a mono pour is 1/2 of what you need. I have built cold rooms using simple Window AC units by modifying the sensors and adding several inches of insulation on each wall and the roof a shed cans be turned into a cool room even a light freezer

My largest one was in my last place and that one did hold and cool up to 3 elk. My current one is less than 1/2 the size but has a larger compressor and coil set to freeze in some shelves to freeze the meat after processing, but is still “ temporary. 
Next season I will put up the inside 2 walls and ceiling and turn on the compressor again.

My first unit I think I used a 12kbtu window system and it was great but I no longer live there. I did use a kit to modify the ac unit even though I could have built up what I have now it was much cheaper and I had a window unit that worked. 

I would look up cool rooms with window ac units or kits to turn a window unit into a cooler (it has been many years) but is legal because the electronics are all that are modified and it works.