Welcome to BYC! Good for you doing your research before you get your flock. Here's some basic information from an article I'm in the process of writing:
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.
Some More Numbers
Height can't compensate for lack of floor space because
chickens don't stack for storage, but there are some useful things to consider about height.
First, the base of the coop needs to be deep enough to hold a reasonable amount of bedding. "Reasonable" is a flexible term , but 4-8 inches is a good starting figure. If you're scooping poop daily you only need enough depth to hold sufficient sand/S
weet PDZ/etc, to keep the poops from sticking to the floor. If you're doing Deep Bedding or Deep Litter and want to clean only a couple times a year you might want room for a foot or more of bedding.
Second, the nest boxes, which are usually 12-16" cubes, need to be above the maximum top level of bedding to keep the clean nest lining from being contaminated by the soiled bedding or you will get poopy eggs.
Third, the roost needs to be above the nest boxes so that the chickens will sleep on the roost instead of in the boxes.
Fourth, the ventilation is best placed above the chickens' heads when they're sitting on the roost -- 8-12" depending on the size of the hen and her comb type.
So, the minimum height to get things stacked up correctly is between 3 and 4 feet high, depending on the slope of the roof and exactly how the ventilation is arranged. Additionally, chickens aren't helicopters so they usually fly up and down to their roosts about about a 45-degree angle. That means that the roost should be at least as far from the wall at the end of their landing zone as it is high.
Additionally, many people like to have small coops raised up both so that the chickens can use the area underneath them and so that they can clean more easily, sticking a wheelbarrow or garden cart under the access door and pushing the bedding out instead of forking it up from ground level. 16-18" is probably the minimum to allow full-sized hens to walk around with a little bedding underneath to absorb the poop while much over 24" will become challenging to clean except for the tallest of chicken-keepers.
A useful article on heights:
https://www.backyardchickens.com/articles/coop-stack-up-how-high-stuff-works-well.73427/
A useful article explaining why these are guidelines, rather than rules:
https://www.backyardchickens.com/articles/how-much-room-do-chickens-need.66180/
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.
- 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
Where, in general, are you located? Climate matters, especially when building chicken housing.