Roosters are not a simple addition to a flock of hens. Are there any specific reasons you want one?
Hens do splendidly without a rooster. In fact, many people who have had a rooster with their hens say the hens are so much more relaxed and content after he's died.
Many people have the misconception that a rooster is needed for the hens to lay. This is a myth. The only reason you would need a rooster is if you plan on breeding the hens to hatch baby chicks.
There are good roosters but there are also ornery, aggressive, annoying, even dangerous roosters. If you happen to have an aggressive rooster, or one who is so crazed by hormones he over-mates the hens, ending up with bald backs and heads from all his "attention", you will be pulling your hair out trying to figure out a way to deal with him.
If you really desire a rooster, it's very simple to add him to the flock. He will be so focused on sex and mating that he will adjust very quickly to his new flock. The hens may, however, have their own problems adjusting to him.
