Do make sure you quarantine him first... so that if he is sick he doesn't infect your flock... keep him completely separate for a while... 3 or 4 weeks... watch him.. maybe worm him, if he hasn't been wormed.... maybe give him some antibiotics if he shows any signs of illness at all... watch his poop, etc.. then, after a few weeks.. then, put him in a cage in with the others, inside the coop or run (run in the daytime/coop at night).... with the food next to his cage... so they can eat "together" and yet not together for a few days or so... his food inside the cage against the side.. with the flock food on the outside against his cage... so they eat head to head.
Then maybe introduce him (loose) into the coop at night.... just be sure he's healthy first.
Search here on BYC "quarantine new birds" and see what the consensus is on how long and all.
Oh, and make sure he's not aggressive (mean) before you take him... you do not want an aggressive (towards people) rooster.
Best of luck... My Barred Rock rooster was the best.