User blog comment:Centuriarch/Different ADC build./@comment-6102571-20140312165621

First of all (didn't even read it completely), Runaan's is extremely situational item.

Second: Every ADC has different builds. They are all extremely similar, but more caster-like carries go for more raw AD early and Arpen next. Those who are more autoattack-based go for AS and Crit earlier. Final builds are similar, but the build order differs.

Third thing: Many ADC's have a certain build that fits their kit better than typical crit-based build, but might lack in lategame damage and isn't used that often because of that. Blue Ez, for example. Another good example would be the Arpen Lucian build that ignores Trinity Force.