The first AP item sHould be Will Of the ancients
then keep in the same way I did
best AP Hp build you dont need armor or magic resist you have runes and a huge shield for that
use E as much as you can near minions try to fight near minions coz the E give you more shield if you hit multiple Enemies and dont forget you maybe OP but keep distance or you will lose the game, try Hurst as much as you can, If someone rush over you just kill him ^ ^
Dont rush near turret coz after 1 turret hit your shield is almost gone
Try use your Ulti on Champ with Lot of HP or With lot Of AD
dont use it on AP Chanmps only if the have low HP and then you of course use Ignite as well
Always use Ulti + Ignite best Dmg Ever
After you Bought Rylai's and Will of the Ancients Use as much as you can coz Slow + the out put dmg is really good

Spam E,Q and W on minions