A couple of Roddy men have participated in the "BigY" yDNA tests, designed it to explore deep ancestral links on our common paternal tree. While these results can not yet be extrapolated to all Ruddy and Roddy men, it currently indicates these surnames have a set of unique haplogroup markers in the CTS3087 and BY390 areas. You can see more of the details of these studies, and relationships to other close surnames, here (managed by another researcher): The Big Tree