I would say that drainage is pretty good but....
if I hadn't used wood chips on it, it would have become impacted and it would be a muddy,slimy mess when wet with water standing here and there.
I had some trees cut down and had them put the chips from the branches in a pile in my back area. I didn't (and no one should) use them before they cured for awhile. I like to see worms and/or other living things in the piles before using.
I began putting the chips in the run when the original grass in the area was pretty much gone except for a patch here and there. I'd wheelbarrow over a couple loads and dump them in a pile. The birds love to dig through and spread them all out.
Kept adding more until there was a nice deep cover over time, then add from time to time.
Every once in awhile I'd go out there with my shovel and the birds get really excited as they knew what I was going to do. I'd turn up a bit of the dirt here and there from under so they could dig through and get the worms.
The soil under there was pliable and wonderful smelling. The birds scratch through what I'd turn over and then it would all be covered again.
One year one of my daughters took a load of the soil out from under the chips to start her raised gardens.
Over time I just keep adding chips from time to time and would also put out all the wood shavings/poo from the inside coop. You just can't beat how healthy that soil is. And NEVER a puddle. Just soaks right through as the soil is so pliable under the deep litter.
If you contact tree services in your area they will often bring you a load of chips when they're working in your area for free.
Just be sure to let them cure at least a couple of months before using - and be sure they aren't bringing chips from poisonous bushes like yews. I just tell them what I don't want (including places that are spraying the trees) and they are happy to leave them.
Here are some photos:
Here is when the original gang was just getting started with some chips from the wood pile.
In the rest of the photos you can see how the deep litter looks in the kennel run. (The lighter colored stuff is some food I had thrown out for them.)