The coach has revealed that the club have been tracking the young Everton midfielder ever since Roberto Mancini arrived at the Etihad Stadium during the 2009-10 season
The Everton academy graduate has clocked up more than 80 appearances for the Goodison Park club despite struggles with injury and last year earned his first international cap for England.
Platt cited the technical skills and potential of Rodwell as making him an attractive proposition for the defending Premier League champions.
"Two and a half years, when Robbie [Roberto Mancini] first came, he has had him on his radar and always liked him," Platt told Sky Sports when asked how long the club had been watching Rodwell.
"He has great technical ability off both feet, can pass it, play in a variety of positions, and has good physique and size."
Platt admitted that it was possible to over-analyse players after keeping an eye on their progress for too long but remained confident that Rodwell would prove a success.
"When you look at a player for too long - you think that could be negative or a flaw, but it doesn't take away the characteristics the boy has," he added.
"I think there is a great deal of potential there and so does Robbie, and we looked at it and thought it is the right thing to do, the opportunity came along for us to do it this summer, at the right money business wise, and we feel that we can provide him with the platform to realise that potential which has been there for a long time.
"We have seen him a few times, we have been to have a look and the opportunity is there, we don't think he has realised his potential and we think we can give him that stage."
Injury problems limited Rodwell to just 14 top flight appearances last season but Platt does not anticipate major issues with regards to the youngster's health.
"We don't think there will be any problems - the hard work has been done," he said.