There's a lot of good maps online, on rpgmapshare and a cartographerguild. I'm wasn't planning on running an AP on roll20, because I didn't know how difficult it would be to recreate maps. But I think I can get pretty close with the tools I'm using. Dundjinni, Photoshop, and roll20. I do backgrounds and tiles on Dunjinni, clean up in PS, and then drop in objects in roll20.