Galloway: "A territorial name from the former Celtic princedom and the modern district in south-west Scotland." (From the Scottish Clan & Family Encyclopedia, by George Way of Plean and Romilly Squire (now of Rubislaw), pub. 1994) If this is true, it would seem to mitigate against any sort of "clan" status, at least in the generally accepted sense of the word, which in turn would suggest that "Rodger" isn't a sept-name, but rather a name, one of several, encountered in the Galloway area. That being the case, I'd tend to agree with Cajun Scot and MacMillan's Son in suggesting that a district tartan might be the way to go.