Hi! It's nice to have you here! I think you will be thankful of not having a slab in case you want to move it ever, plus the dirt and natural microbes will help break down poop and anything better on no slab. Just add some dry organic material and you can cultivate compost for 3 families, too!
I hope your chicken project goes well! Let us know if there is anything we can do to help!
Thanks for joining and welcome to BackYard Chickens!