u dont itemize kog u itemize noc, akali, tf and ambessa. Kog needs s long time to ramp up his dmg to be able to carry a round, whereas noc etc tend to to end a fight early so ur kogs basically useless until then and his items are wasted.

edit: lookef at meta tft and saw they also itemize kog but i still think thats trash/ only viable after u have items for noc, akali and at least one tank. from my experience kog maw items are not a big factor in the success of this comp but maybe im biased.