Country Dreamin' :
First off, i didn't realize how expensive pre-fab coops and even garden sheds were! How the heck i am going to afford this?
Buy secondhand, a shed or playhouse from craigslist etc. Or, scrounge up (as opposed to 'pay full retail price for') some materials and build something yourself.
Secondly, i am having a hard time understanding the space rule. I have read 4 sq for every chicken. It seems like if i want to have 8 layers and 10 meat birds i am going to need to have a GIGANTIC coop!
Honestly there is no magic number. A lot of BYCers keep their chickens at 4 sq ft apiece indoors plus suitable outdoor space; some keep them in less space; personally I have tried that and seen how they behave and will never keep them at less than 10-15 sq ft apiece *plus outdoors*.
If you wanted to give 4 sq ft apiece to 8 layers, that would only be a 4x8 coop, not very big at all! (Plus a run, or free range, or ideally both)
Meat chickens are a bit of a different thing... if you mean CornishX (supermarket style) birds, they can more-reasonably be kept in crowded conditions than layers can because they do not move around as much and also will only be "enjoying" your coop for 6-8 weeks before you kill and eat them. So a lot of people will keep them in 2-4 sq ft apiece TOTAL, and they do reasonably ok although sanitation/air-quality is a GIANT NIGHTMARE and you WILL NOT WANT THEM IN YOUR LAYER COOP, I am serious. (Even CornishX do benefit from more room and an outdoor run, though, at least health- and happiness-wise, although moving around more can mean slightly lower feed conversion efficiency). So if you wanted to give your 10 meaties 4 sq ft apiece total, that would mean something 4x10 or 5x8.
A whole lot of the space-requirement thing depends on your climate though. If you live in, like, Hawaii, and LITERALLY the chickens will never ever want to spend much of a day indoors because it is so yucky out, then truthfully all you need is room for adequate roosting space (8-12" per chicken is plenty -- this pertains only to layers, not meaties). If OTOH you live somewhere with viciously cold or snowy winters, then it is hard to predict what your particular chickens will do but quite often they will not want to go outside much if at all for days or even weeks at a time, and it is a real good idea to give extra space so they do not start killing each other.
The two main considerations space-wise are a) the more crowded they are, the more burdensome sanitation becomes and the harder it is to ensure adequate ventilation; and b) the more crowded they are, the likelier they will start engaging in pecking/cannibalism -- yes, they WILL kill each other if they happen to be grumpy that day or if they peck someone enough to see blood and get all excited about it -- and note that pecking/cannibalism problems cannot *always* be solved by providing more space, sometimes it becomes such a habit that the only thing to do is make a whoooole lotta chicken n dumplings and start a new flock.
But honestly it is not like you are proposing to have SO many chickens... I do not know what climate you are in, but for most peoples' purposes you'd do fine with a 4x8 or 6x8 (or larger if you can get it!) layer coop (e.g. secondhand garden shed) with a 5x8 lean-to roof built off one side to make a 3-walled pen for your meaties.
Good luck, have fun,
Pat