Roth lived a quiet lifestyle, and Michael knew it. Part of Roth's facade was that he was sickly and reclusive, so it was more likely than not he would be home in Miami. That aside, the Corleone's people in Florida could have easily determined Roth's whereabouts. Michael's visit was supposed to put Roth at ease, and to give Roth a sense that Michael was panicking after the hit. In their conversation Roth says he knows about what happened, and Michael then tells Roth that Pentangeli arranged the hit. This is exactlyt what Roth wants to hear, and when Michael asks for permission to kill Pentangeli, Roth tells him what a thoughtful and respectful "young man" he is. So it is possible to think that the Roth meeting was not prearrranged.