If you start getting condo and high-density encroachment into the older subdivisions (and that's probably more likely along the commercial corridor) you could see some increased runoff. But this is not a flood zone and we're not talking about a huge creek. During those 2009 floods the normally dry wash next to our property was a raging river (and got into our crawlspace).
I cruised around the Roswell website for awhile, but didn't see anything in the development plan that had an impact on this particular property - other than it being within the Alpharetta Highway commercial corridor. Source?
It is identified on the city maps as a flood zone, which it obviously would be by the simple geographic fact that the lot is located at the confluence of two creeks.