You are getting a lot of good advice here. Not to disrespect anyone ele, but really, really listen to Pat. She knows what she is talking about.
1. We have a poured cement slab covered with OSB on the floor. Not all the pieces are secured.
You seem to be taking a lot of care with your coop, so I am going to assume you will keep your floor dry, that water will not come in from the outside or leak in from the top. If I inherited the flooring that you describe and I was in Iowa, I'd probably tear up the OSB and dump 4 or 5 bags of pine shavings in there. You don't even have to spread it, but if you want to take that pleasure away from them, you can. 4 or 5 bags is probably not enough for a 11 x 12 coop, but it is enough to start. Just dump another bag in there as you see a need. As long as the wood shavings are dry, they are a tremendous insulator. You really don't have to worry about the concrete being cold in the winter as long as your shavings are deep enough. You can make it as complicated as you wish. You have that right. Or you can make it this simple. If you had a small elevated coop your situation would be different, but with a coop this size, the shavings kept dry, and especially if you use a droppings board under the roost to keep a lot of the poop out of there, you will not need to clean this out more often that once a year and you may be able to go longer than that.
When it is time to clean it out, just shovel it out. A rake will work fine to get the last of the bigger stuff and make it easier to shovel out. If you really feel you have to, you can try to sweep up the dust, but you really don't have to. Tha dust makes a great addition to your compost but it will not hurt anything to leave it behind on the bottom of your next layer of wood shavings. Whenever you do clean it out, wear a dust mask. If you think the paint fumes were bad, just wait.
2. Run is up next. What needs to be out there? They will have water and food in the coop. Do they need water outside? Food outside? I think we will use sand for the run.
I think sand is an excellent choice for the run. It dries out quickly, they love scratching and bathing in it, and they will get a lot of grit when they eat it. Just make sure your drainage is such that rain water runoff does not run into the run.
Where you feed and water is your choice. You can make arguments for either or both. In Iowa, you will probably want to water inside in the winter to help keep the water thawed. I used a black rubber bowl and watered outside during the winter. If water froze in it, I just turned it over and stomped the ice out. I found that if it was in the sun, it would keep water thawed down to the low 20's but it was normally frozen in the mornings. I like to water outside to keep the wood shavings drier, but people manage both ways. I personally like to feed outside also. I have not had a serious problem with it, but some people wind up feeding a lot iof chicken feed to wild birds if they feed outside. I like it outside so they spend less time in the coop, which decreases the amount of poop dropped in there, and I don't want to encourage rodents to enter the coop. We all have different conditions and management styles. This is the way I do it. I don't consider mine any better or worse than other styles.
3. We want to use hardware cloth and plan to use the apron method. We think it should be tall enough to walk into (right??) What is the maximum size of hardware cloth that would be safe to use on the bottom and on the top. The bottom 2 feet, 3 feet how far up to go with the smaller stuff??
Sounds like you will cover it. It should absolutely be tall enough to walk into. I guarantee you that you will regret it if it is not. And remember to make it several inches taller than the tallest person that will go in there. When you step, you rise up, sometimes several inches. And when figuring the height, remember to include the thickness of your cross braces for the top. If you hit those, you hit the bottoms, not the tops. Yeah, I know, but some people forget that. And the aprons are a great idea.
For me, aprons, tops, sides I'm real happy with 2" x 4" welded wire. That will keep out most serious predators. Snakes, rats, and some weasels can still get in, but I seriously doubt you can keep them out of a decent sized run anyway. They are real hard to keep out. In addition to the 2" x 4" welded wire, I strongly suggest using something at least as small as 1" opening wire around the bottom 18" or so. If it comes in a 2' wide roll, I would not cut off 6" to get down to 18", but if you want to save money and split a 3' roll, it would work. It keeps the chickens from sticking their heads out where a predator can take it off, it keeps some predators from reaching in, and it will keep baby chicks from leaving the run. I don't know if 1" is small enough to keep bantam chicks in, but it should keep large fowl chicks in the run if you go that route for raising them. If someone says that 1/2" is better than 1" openings, I'm not going to argue with them, but I think 1" is small enough. Make sure the chicks cannot get out under the smaller stuff. Chickens will scratch around it, so if you are going to have baby chicks in there, I'd suggest burying the bottom of the smaller stuff about an inch. Should be enough with the apron on the outside.
Good luck with it. I think your chickens are going to like it.
