Well, they sleep on a roost, not on the floor.
You'll find that the soil will get quite stinky unless you scoop the poo daily. It may also get compacted, making it difficult to clean. I would suggest either sand (if it is dry, wet sand is worse than soil) or pine shavings. The pine shavings can compost right there if you do the deep litter method, or you can remove it and add fresh periodically.
Concrete is a good base to use though, prevents predators from digging in and reduces the places where rodents can take up residence. But you definitely want something other than soil on it.
Hay is prone to mold, Straw is dusty and picks up odors easily. Horse stall pellets are nice if you break them up, but sometimes the birds confuse it with feed. All 3 of those options are the top of the list for causing impacted crops if they do eat it.
Plenty of people mix bedding types. Depends on how you want to clean it. Clean the whole mess of it out twice a year and use in the garden, or scoop daily/weekly. Or just clean under the roost and let the rest compost.
I have sand in the coop that I scoop daily, takes just a second. The run is deep litter pine shavings, I add about 5 bags of pine shavings a year. Haven't had to remove any yet and there is no odor.