you can always build your own coop, with any wood you find. You can seek the highways for pieces of wood, and an internet site I looked up said you can also go to a construction site and ask kindly if you can use any unneeded parts of things to build a coop.
It's great you are raising hens for eggs.
Welcome to the site.
Well, the area of yours being 12x20 should work out, all you got to do is work out how many hens you got. And hens do like to have choice in where they roost. I been having chickens, raising them for two years now. I just joined this site like last month.
Usually, starter chickens are considered to be chickens like Rhode Island Red, or Barred Rock. They are easy to obtain anywhere in USA practically, and probably other places too, maybe. Anyways, those are easy to raise breeds and could either be free range or cooped up. I have always free-ranged. Having your own chicken eggs tastes better than store-bought eggs.
If you get day-old chicks, you will need to put them in a small bird cage and keep them warm, in a warm room, like with a heater. You need a chicken water feeder and bird food and bird food feeder. They need to have a flooring that they can grip and not slip. Such as hay, a blanket or towel or towelette(put a few to cover ground.) they will poop on it, but I washed it just once and it comes out fine. use an old towel or blanket would be better. I used just any towel we had, but not a good blanket, just a medium-sized orange one we never use.

They supposedly can slip on newspaper, but I once had baby chickens on that and I had no problem, I didn't know that it could harm their legs at that time. You have to change that newspaper frequently too. Well, I had 12-15 chicken babies then. For a towel, it takes 2-3 days to have to refold or wash.
When in a small cage, my babies didn't have a chicken feeder in their, too big. i used small container bowls but they always spill it.
When your birds start to grow feathers, then you can put them in outside in their coop. Hmm, maybe you need to have a heated coop for them to survive right away outside. But I just love my chickies. Put a heater in the coop. There's a word for another option most people do: brooder. It's a large tin holder that has two lights to keep them warm without my heater, but my heater worked for two years just fine. It was when the heater was off, I had a few suffer hypothermia from them spilling the water. I saved 2 chicken babies from putting them to the heater sometimes and my chest alternatively till it got warmer and breathed. You need to be prepared for that, because it happens a lot with chicken raising, somehow you lose chickens to predators or health problems. It is sad. If you feel real sad, that just means you are dedicating yourself a lot to raising and caring for chickens. I love my chickens I have today. If none of them died, I'd have like 30-35 chickens now, but I only have 15 now, thanks to 6 new babies.

and a guinea included.
And P.S. dont be jesus-freak to me. I didn't need Jesus to help me raise chickens. I have thanked God for my 6 babies though.