best items for pushing towers

im experimenting and trolling with tf im actualy kinda stuck when chosing itmes runan is a must, and so is nashors tooth and wits end i can completly rework the build but i need some advices about items which are goot for killing towers because after wrecking 3 minion vawes under 10 sec im just pecking a tower for half of a minute (its worse when i meet an inhib cause i cant use blue card on it)