0/12/18, Taking grasp of the undying, and the mana regeneration mastery from the cunning tree (You'll need it, trust me)
Runes are pretty standard AD/Armor(or HP)/MR for me, I don't even bother with Attack speed runes on Illaoi because her base attack speed is so fucking abysmal.
Items I like on her depend on how well I do in lane, if I'm winning super hard I like to go Cleaver first, into Steraks, into tank items. If I'm not really killing my lane opponent or I'm outright losing, I like to go into Iceborn Guantlet first, since it gives me beautiful 20 CDR, a reliable CC in the form of IBG's version of spellblade, a fuck ton of mana to spend on whacking people with tentacles, and armor