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It's really difficult to buy any coop that's truly appropriate for keeping chickens. The OverEZ coops have the reputation of being better-built than most prefabs, but they are woefully under-ventilated and claim to hold many more chickens that is actually appropriate. But I've seen people who were happy with them after fixing the ventilation and getting the actual dimensions (not counting the nextboxes), so as not to overcrowd them.
That said,
Where, in general, are you? Climate matters, especially when it comes to housing, so if you put your location into your profile people can give better-targeted advice.
Also, it's helpful to have your own thread when you start your build so that people don't get confused about who is building what.
I haven't done a metal shed conversion, but there is no reason that it couldn't be done well -- the main thing is the ventilation.
A floor is not necessary. The Deep Litter method (moist, actively composting), works best on a dirt floor. But do put a predator apron around the outside.
Here is some basic information for you:
Repecka Illustrates Coop Ventilation
The Usual Guidelines
For each adult, standard-sized hen you need:
- 4 square feet in the coop (.37 square meters)
- 10 square feet in the run (.93 square meters),
- 1 linear foot of roost (.3 meters),
- 1/4 of a nest box,
- And 1 square foot (.09 square meters) of permanent, 24/7/365 ventilation, preferably located over the birds' heads when they're sitting on the roost.
6 hens
- 24 square feet in the coop. 4'x6' is the only really practical build for this given the common dimensions of lumber. If you can't walk into it, put the access door in the middle of the long side to make sure you can reach all areas of the coop because a stubborn chicken WILL press itself into/lay an egg in the back corner where you can't reach.
- 6 feet of roost
- 60 square feet in the run. 6'x10' or 8'x8'.
- 6 square feet of ventilation.
- 2 nest boxes, to give the hens a choice
8 hens
- 32 square feet in the coop. 4'x8' is approaching the limits for a non-walk-in coop even with the access door in the middle. 6'x6' should be walk-in because even the tallest chicken-keeper won't be able to reach the far wall.
- 8 feet of roost
- 80 square feet in the run. 8'x10' is a nice looking number but, remembering the common dimensions of lumber, a roomier 8'x12' is actually easier to build. 6'x14' looks good on paper but would require a lot of weird cuts.
- 8 square feet of ventilation.
- 2-3 nest boxes.