Experimental and overall non-meta but it is quite strong since Illaoi scales with AD and it is just best for her, lethality also works but that is not enough for Illaoi, but I guess you could go for a hybrid of lethality and AD, like going Manamune on lethality build, etc.

Have fun and mind it's about hitting E and just destroying the enemy, in the late game, you will be able to send 99% echo to the enemy player, 1 slam will deal 900 AD and just super strong. In early games just you can play aggressively but know your matchup and what counters you. This is non-meta just an experimental build so I don't recommend using it in ranked matches if you haven't played it before. You can also go with Dark Harvest instead of Conqueror but I just like Conqueror in this instance. Change some stuff and find better items you can use so it is truly an unbeatable build.