your situational items are up to you. What I do is rush blue sight stone first and then maybe frost fang. your main item is ardent censor because your W when used near allies will give everyone the attack speed and on hit buff because it is a shield. You can then rush lich bane for extra on hit damage. By this point you are hitting the enemy for a lot of damage. You probably just want to buy items like deathcap or rylais for additional slow. If the enemy is building mr you can buy void staff too. By the end of the game your damage to champions is probably close if not more then your allies which is good since you are also a support!