CTKen has covered the 4/10 rule of thumb well.
Tho I think that 1 foot of roost per bird is sufficient....the 4/10 rule is a bare minimum in most cases.
Free ranging doesn't really allow you to skimp on coop space unless you live somewhere where it never rains or snows, and run space should be as large as possible if you plan on confining them while gone on vacation....or have a predator event that deems confining to run prudent.
What is your climate? Putting your location in your profile can help folks give better answers/suggestions.
How many birds do you plan to have?