When it comes to AD items the itemization is clear, there are the bruiser items such as black cleaver, trinity force, titanic hydra, etc, the assassin items are clear as well, duskblade, youmous, etc, and the ADC items are all the crit items. League has tailored items to the needs of the champion classes that use AD.
This does not seem to be the case for AP items. There is a large variation with AP items but there doesn't seem to be role specific items. The ap items seems more attuned to play styles such as damage over time with rylas and liandrys or going for a burst build, such as ludens, Morellos, Deathcap. There is not a clear division of items for AP users, making them all fit in the "mage" role. There are definite roles within AP, Poke (Xerath), Control (Taliyah), Assassin (Eveyln), Juggernaut (Mord). The AP items should be more specified to these roles, the assassin items should give access to magic pen and burst, the control mages should have access to health and cc, and the juggernauts should have access to damage over time. This is of course just an opinion and I believe that it would help better balance AP items.