do this build, the last item you can choose depending on the game. like mejai if you're killing many enemies, zhonya's hourglass if you need more durability. or another rabadon. anyway. this build will give you 600+ ap without the last item. i usually make a second rabadon. and with consumable items i get 870 ap with magic pen. it means op, i choose the teleport spell to teleport to a under attack lane if i am far away from it. with my ult i can destroy minion waves in a sec. but you can switch it if you want. i usually mid to farm and kills the enemy without distractions.