Welcome to BYC!
That's quite a LOT of chickens. Have you raised chickens before?
The Usual Guidelines
For each adult, standard-sized hen you need:
- 4 square feet in the coop,
- 10 square feet in the run,
- 1 linear foot of roost,
- 1/4 of a nest box,
- And 1 square foot of permanent, 24/7/365 ventilation, preferably located over the birds' heads when they're sitting on the roost.
That said, from a behavioral/social standpoint a large flock in a large coop doesn't necessarily need as much space per bird because any given hen has more space to put between herself and a harasser. But each bird still generates just as much poop so sanitation issues could pile up with chickens kept at a higher density.
Using the numbers above, for 50 hens you'd need:
- 200 square feet in the coop -- at least 10 x20. 12x24 or 16x16 would work better with the common dimensions of lumber and maybe allow you some built-in storage space.
- 500 square feet in the run. My 100 feet of Premier 1 electric netting encloses about 600 feet of space and I will tell you that only 9 chickens managed to destroy all the grass I could give them through moving the fence around a core area in less than a year.
- 50 linear feet of roost. With large flocks it's good to arrange the roosts so that groups of dominant and subordinate chickens can separate themselves.
- ~13 nest boxes
- 50 square feet of permanent, 24/7/365 ventilation, preferably located up at the roof level.
So you can see that you need to be thinking small barn rather than "coop" -- and that a pallet build is going to be problematic at that size.
Metal buildings can be tricky to ventilate unless they're actually designed as barns (metal pole barns are common in my area). A 1-car carport might be a good starting place.
This is my Open Air coop, which is 16x16 -- just to give you an idea of what that kind of space looks like.
https://www.backyardchickens.com/threads/large-open-air-coop-in-central-nc.1443812/
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