I would suggest the normal space requirements you see on BYC. In my case, I decided to reuse a coop & pen I had built for Silkies. My bachelor coop is 6 ft x 7 ft and the run is 8 ft x 10 ft. I currently have 9 full sized roosters in the bachelor pen.That's a good idea. When you say bachelor pen, how big are we talking? I have seen someone free range and they lock up their roosters in something smaller like a large dog crate. I have room, not so much materials but I'd like to make it work if I can
There are a lot of creative ideas on BYC for making a cheap/free, but secure coop out of various materials. Do a search and see what you come up with that meets your needs.