How big should a yard and house be for 128 chickens?

Its party time in the hen house (to be) !! Best of luck in your endeavor!!

 

4 square feet per bird x 125 birds = 500 square feet of coop
10 square feet x 125 birds = 1250 square feet of run

Maybe 20' x 25' for the coop plus 50' x 25' for the run . Do you already have some coops and runs? You could keep smaller coops and yards, perhaps one per breed?
*Whew* That's an awful lot of chickens! I can't even imagine!

 

OMG 125 plus chicks or chickens all due the same time wow. Don't go and burn yourself out. I would do this a whole different way if I was doing this. If your starting out with chicks thats a lot to tend to at one time. You will have to be carefull not to crowd them, making sure you have the lights to keep them all warm but not hot. Fresh feed, fresh water, fresh bedding is just a few things you will have to be on top of. You will have some that grow like crazy and then you will have what is a runt which you might have to put in another place to keep from being stomped on. I really hope you do good on this but for your first time I would of practiced on fewer birds. I would of gone to the swaps and ASKED questions on whats good for the chicks. I wish you the best of luck but don't let this burn you out on raising chickens if you have a bad turnout. Ask questions and when you think you know what you need ask again there are MANY fine people here at BYCs that will be happy to help you. As far as BO chickens had them they were very nice calm birds but I didn't like the food-egg ratio so I sold mine. If your looking for eggs production on your birds I might of gone with RIR, BA, White leghorn and theres a few more breeds that are egg laying fools. Also if your going to ever want to set these chickens eggs you might want to keep their breed true and only keep one breed per pen. Also at these swaps you can find most of the birds you said you plan on having. Support the swaps because you get better birds, healthy birds, no shipping cost, and you help other chicken/pet lovers share their stock. You get to meet the person that raised the birds you want and you get a chance to chit chat with the sellers and pick their brain for more chicken ideas. Again good luck.

 

That's like "how long is a piece of string".

It just depends how much space you want to give them.

Remember that with that many chickens housed all together, when something goes wrong (disease, parasites, cannibalism) it will go very very wrong very very suddenly and be near-impossible to fix aside from making a lot of soup and then starting over.

Good luck, have fun,

Pat