/diy/ - Do It Yourself

Question related to issues with my detached garage:

The first thing is that the slab the garage is on is in horrible shape. There are cracks everywhere, large chunks missing, exposed aggregate, etc. Is this something that is repairable in a DIY situation, or would the slab need to be broken up and removed before a whole new slab is poured? I don't know a ton about concrete work, but to me it seems beyond saving.

The next semi related question has to do with moisture. The plywood on one side of the ceiling in the garage is always wet. Like completely saturated with water and drips a significant amount on my car. It's only the north side. The south side is totally dry. I originally thought it was the roof so I had a new one put on. It continued staying saturated and dripping so I called them back to look. They lifted the shingles on the garage, and underneath the felt paper and everything is bone dry. They redid the cap to face the opposite direction in case it was wind/rain related but that made no change. My thoughts are that water is seeping up through the cracks in the slab when it rains, evaporating, then forming condensation on the ceiling of the garage. The slab is definitely damp so I think this may be the issue. Since my slab is in such horrible shape, if it's beyond saving could I at least put some sort of sealant on the floor to try keeping the moisture out, or would that be a waste of time?

This isn't my forever home and I'm planning to use it as a rental in a couple years. I'm unsure about how much money I really want to put into it at this time.