3 ArP items is when the enemy has ONLY armor items or heavy armor team and you are forced to focus them.
Black Cleaver is nice if your team is full AD and nobody has it because the passive shreds armor allowing your allies to take benefit of it.
Yomama's Ghostblade is the best against squishies because it has more flat armor pen, the active blends well with BotRK and the crit chance allows you to deal some nasty crits during duels or when sitting there doing AA.
The most common builds are Yomama's\BC+BotRK+Hydra(BT works too)+LW+Defensive item, or you can go balls deep and go full AD.
There is a crit variation where you swap hydra for an IE paired with Yomama's gives you 40% crit chance, personally i go with this build if the enemy team has any kind of way to nullify your ult as damage dealing ability (GA stacking, Zhonya's, QSS), might as well try to instakill focus with crits right?