Do a search or go to the learning center up at the top. TONS of useful information there.
We need WAY more info to give you good advice, so check out the learning center first. People will want to know--how many chickens, what kind, hen to roo ratio, etc.
1 nesting box for every 4 hens.
1 foot roosting space per chicken
2 square feet coop space per bird.
Build your coop large enough to house twice the number or chickens you think you will get, total. Or:
1-Decide on the # of chickens you want
2-Build the coop big enough to house twice that.
3-To start with, buy half as many chickens as you think you want total. This will help with chickenmathitis all newbies get.