Eddie,
I strongly suggest you spend some time at backyardchickens.com, linked in RayJay's post. There is as much wisdom about chickens there as there is about tractors here.
Elevated coops are easier to predator-proof than ground level. That's why you see some many designs with elevated coops. The area under the coop gives them some shade, too. Look at the one at backyardchickens call the "Wichita". That's roughly what I built, though mine is on runners where I can move it around.
If it's just the two of you, 4 or 5 chickens will keep you covered in eggs once they start laying.
Just passing on some personal experience here. My first batch of chickens we raised from day old chicks. They put themselves to bed in the coop like clockwork. Something got all but one of them all at once, during the day while we were away. Never have figured out what happened, there wasn't a single feather left behind. Anyway, I replaced them with a couple of hens that were already laying and some pullets that were at point-of-lay (18 weeks old, just about ready to start laying). Those older chickens just wouldn't adapt to the coop and regardless of how long I would lock them up, when I started letting them free range again, they would nest in the trees instead of going into the coop. That worked for several months, but finally a coon found their tree roost and got them all.
So, my point is, if you're going to free range them (and I suggest that you do), start with day old chicks. It's a 5-6 month wait for egg production, but there will be less squabbling about pecking order and you can teach them where to bed down.
And, I'd ditch the concrete floor idea. Just cover the floor in rice hulls and change them out every 5 or 6 weeks. Stockpile the rice hull/chicken manure mix and use it on the garden next spring. Chickens habitually scratch the ground, and they will tear their feet up on concrete.