"Voice Of Experience"
"PAINT THE DAMN FLOOR (SLAB) BEFORE ERECTING THE BUILDING!"
It'll be a helluva lot easier.
Actually, I couldn't care less which way you roll. Paint, seal or leave bare.
When we built our home, because of my progressing disabilities, we decided to just stain and seal the concrete.
BUT....
We didn't do it before we got the house dried in!
What a mess!
Degreasers!
Etchers!
Volatile chemicals, etc, etc!
Yeah, select a "non-slip" surface.
Even with a sealed, painted floor, protect it with cardboard, plywood ($'s

!) or something. Stuff like antifreeze, brake fluid and power steering fluid can peel paint, sealer or stain right off.
In fact, be aware that regardless of how cautious you are, something WILL eventually screw it up! LOL!

!
Cat litter!
Get the really cheap clay type.
I spilled about a pint of motor oil on our living room floor during construction. Poured a butt load of cheap cat litter on it and it sucked it right up. No problem.