I think a poured concrete roof is out of the picture. I could certainly get a concrete pumper hose in there, but I don't think I want to deal with pouring four inches of concrete into a eight inch space. Not lots of room to work with. Also, I would like to have overhead lighting in the vault. The concrete will make working with the wiring and finishing the inside ceiling more work.
What do you think of a steel mesh, similar to chain-lnk fence, along the bottom of the floor joists secured to the top of the cinder block walls to provide some overhead protection? It's not as secure as poured concrete, but it's better than dry wall.
I'm trying to do this myself for a reasonable amount of money. If a large, high-quality safe will cost me about $2,000 installed, I'd like to keep the vault price around $3,, including the door.
Can the cinder block bet set directly onto the poured concrete floor? Does the floor need to be drilled for re-bar to prevent the blocks from sliding or being pushed out of place? Same for the wall?
Would laying a steel frame track on the floor and wall to secure the blocks be necessary or worth the effort?