I think I can define all my polygons as sets of lat/long coordinates in my database and programmatically loop through those sets of coordinates to create polygon overlays to put on the map.
Or, it looks like I can take an existing ESRI/ArcGIS shapefile and convert it to KML and use that for a custom overlay. This seems more difficult to me and like it may be problematic if I need to tweak my polygon data if I don't like what's in the shapefile. But I have no expertise with this, so I'm not sure.
At any rate, I don't know the advantages or disadvantages of either approach. Or if there's another approach I should consider.
Any guidance or words of wisdom are greatly appreciated.