It seems that the first item for mages is locked into Ludens Echo most of the time, if the mage wants to use glacial augment to land a cc ability they build a GLP, or if they are ryze they build archangels. For the champions that don't have mana or don't need mana they usually build a protobelt. ROA has fallen off the face of league, the only champion that I know that builds it anymore is swain, and I don't see swain that often outside support anymore. The reason i think people aren't building ROA any more and it isn't that it isn't gold efficient, being 97% gold efficient when you buy it, and 156% at full stacks. An interesting mechanic they could put on ROA would be scaling CDR, like the scaling CDR in runes. ROA is currently one of the cheapest AP items in the game and still no one buys it.