follow up...Ive seen as many as 9 birds in a coop your size....but keep in mind you will be cleaning it every other day, will probably have bug problems, pecking, and a higher incidence of other health issues including respiratory problems.
I usually tell people that want chickens to plan for a coop they can afford then borrow enough money to double that. LOL
I got really lucky we had a 10x20 shed that I am using part of now and will probably end up converting the whole thing over to coop next year. I can envision adding on to my run as well to rotate more often and keep the clover and flax growing. I figure my eggs cost me around $3 per dozen when all is said and done. I sure aint in it to save money, LOL