If he is a young rooster then 8 would be ok, if he is 3yrs. old or more 5 is max for him. Usually breeding pens hold 3 or 4 top hens with a rooster, for specialized breeding. Just to have fertile eggs you could run up to 10 per rooster, but every egg may not be fertile. We make a breeder pen for up to 4+1, check out my facebook page below for ideas.