I use a chicken A-Frame tractor, Once they are 2 weeks old.. Having a MUCH colder side of the "brooder" while stil having a warm light to warm up under, Causes my chicks to be much healthier then when I keep them inside for 5 weeks.... My last two batches (16, and 17) Were kept outside once they hit 14 days old... and they are MUCH healthier than my other birds.
cats are very resoursful the chicks would stay in but the cats i doubt will stay out!!