i build him tanky/support, if i actually play him (i don't main him at all, but i know enough of this game to know what a champion needs. since i play him tanky/support, i don't take tear of the godess for the mana, since i'll just get the mana from frozen heart). fairie charm, 3 wards and 2 health potions for starting items. fairie charm turns into philosopher's stone, then boots, then heart of gold. after that, cdr boots or mercury treads, most likely mercury treads. for the first core item after the boots and gp10, i get aegis of legion. then i'd probably get frozen heart for the armor and mana. after that, turn your philosopher's stone into a shurelya's, then heart of gold into randuin's. buy wards whenever possible, since you're the support.
if that was unreadable, then here:
fairie charm, 3 wards, 2 health potions.
fairie charm into philosopher's (gp10 helps you finish items without much cs)
regular boots
heart of gold (same as philosopher's)
mercury's treads or cdr boots, most likely mercury's
aegis of legion
frozen heart
philosopher's into shurelya's
heart of gold into randuin's
always buy wards since you're the support