What should I use for the floors of my run?

[Knock Kneed Hen]

I have a concrete floor in my coop and was thinking of using sand too. Only problem is is that my floor won't drain. Would it start to smell if I'm just raking the poop off the top?
Would I have to change it out every so often? Why are there so many darn choices when it comes to chickens?

 

[Miizki]

Hmmm that's interesting. I wonder if that would work with the concrete floors as well.

 

[Bryceeast]

Pea gravel gets really hot