My decision for predator proof run : Raised (at least 12 inches) plywood floor with vinyl floor covering and covered with sand. Surrounded by 1/2 inch Hardware cloth with 2x4 support stucture that is three feet tall and re-enforced (braced) at least every two to three feet. All hardware cloth secured with screws/caps and staples and then Trimmed over with screwed on wood. Add electronic flashing red LED at bottom of each side and real padlocks for all access doors, windows boxes etc.
I live in major uban area very near a very large county park. I have a fenced in yard> my main predator concerns are raccoons, people, rats, snakes (primarily black racers which are excellent climbers and love eggs of any kind), feral cats and owls/hawks (listed in order of lkelyhood of predadation).