Sky is the limit! or your budget is -
I've seen people use bales of straw for a coop - or an old school bus!
For me personally - I bought a store bought shed - less expensive than building one though not as nice (but heck its going to be covered in chicken poop - how nice does it need to be!).
You need to consider size - 11 adult chickens take up a lot of space.
Summer is no big deal - they can have a tiny space for summer - they will only sleep there & maybe lay eggs if thats where your nest boxes are. But the dead of winter when its 5 degrees out & the wind is blowing - they wont go outside. If it's too small in winter they will start picking on each other & it can really be a mess - so............you want no less than 3 sq ft per adult bird - so your coop should be no smaller than 4x8.
You want plenty of ventalation but also protection from the wind (think winter again).
Also - it needs to be closed & locked at night - raccoons, oppossum, fox, hawk, owl, snake, weasel, neighbor dogs, flying monkeys, terrorists and in-laws all eat chickens! most of those come out after dark - the girls will put themselves to bed - but someone must close the door. Speaking from experience here - I've had to replace my flock several times.