Wood – Reclaimed floor boards vs roof boards: what’s the difference

Anything rigid you put over a flimsy structure will be destroyed over time because it won't have the support it needs. Most tiles (except plastic/vinyl) don't handle bending well.

Self leveling compound doesn't add rigidity, it just makes a smooth top surface.

You need to fix the structure first. That means going down before you go up.

Installing hardwood flooring over concrete is generally not advisable for multiple reasons. Two of these reasons are: 1) oftentimes the concrete is moisture permeable, which means that any solid wood floor installed directly to the floor will buckle irreversibly; 2) typically solid wood floors are nailed to the substrate, which is not an option with concrete. One can install 1.5" sleepers on top of the slab to provide this nailing substrate, but this affects significantly things like ceiling height, door height, countertop height, etc. So this is generally not done as a remodel project unless you're remodeling the whole thing. One thing I would recommend as a compromise is finding some way to seal the slab, say with an epoxy paint, and then gluing an engineered wood floor to it.