Builds have (almost) nothing to do with damage output. Warwick builds ad/as/tank, but his passive does magic damage, his ult does magic damage. Corki's passive makes 75% of his auto attack damage deal magic damage instead, most of his abilities scale with AD, but they do magic damage or mixed (in case of his E). Evelynn builds AP (if played the way Riot wants you to play her) , but her E, which happens to be a large part of her burst, does physical damage. Mordekaiser's Q and E scale with some AD, but they still do magic damage.