I have a dead-simple coop. Like you, I had a shed to work with, though mine was a wooden one with a decayed floor. Chickens are really darned easy. I screwed a couple of 5-gal buckets to the wall about 8" off the ground with their openings pointing out and left about 1/3 of their lids intact as a lip on the bottom. The hens lay in there. You don't need to make boxes for each hen to lay in. They'll happily dump their eggs on top of the previous hen's eggs all day long. If I didn't have the shed, I would have built something simple. Even a little playhouse-sized building would work. As long as you can shut them in at night so predators don't nail them, you'll be fine.

I throw straw on the floor occasionally. They don't "pee," actually, they take care of that in their droppings. If you just freshen up the floor once in a while, you can let the layer get as thick as you like… then have a big chicken coop clean out day once in a while.

Coop-to-run ration? Roughly 1 part coop… 3 parts run. I've got a run that's about 20 x 40' or so… outside a henhouse that's perhaps 10' x 20.'