Building AP Mordekaiser can be one the most ideal choice. Mordekaiser is a mage. With above build, it will take his AP to 300+ and increase his magic penetration. If not pushed in the middle, and able to grab your first 3 kills without feeding them first, you can mostly take down all the other players in the game.

Concentrate on pulling them with E and then bonk with Q. Back down for a bit. Let your abilities load and perform same until they low and hit them with R.

When you fear you might be ganked, ofcourse backing is the best way. BUT... if you have your R ready, go in the top laner is half the health. With this build, 90% you will kill both. One with your R and other with your high AP.