i've had the most success building rightous glory 1st item (against ad, and even if its not the first item i build RG as 4th item, i think is core with swain, the pick potential is absurd) abyssal mask (against ap),defensive boots, zhonyas, rylais and a liandrys torment. 30% cdr in the build, so u can spam your Q quite often, for runes i take sorcery (phase rush, ultimate hat because his ult has a really long cooldown, this helps a lot in team fights ,celerity for early MS, and gathering storm since in early i focus on farming) and inspiration (stopwatch and cosmic insight). this makes swain a tank with ult frequently and great pick potencial and utility with rylais slow and rightous glory. i level up Q at 1, max E, i dont use W in lane 'cause even if it hits it cost a lot of mana, i put first point in W at level 5 or 7. sorry if i made any mistakes, english is not my native language.