this is my first time making a build so please be gentle.
i really like this build because you dont have to go back all the time and get mana, and that makes her good at the mid, cause she get many creeps kills.

i like to start out with (philosopher´s stone)cause u can keep it all game long, and it makes good many in long term distance.
sorcerer´s shoes because of the magic pen.
rod of ages is good because u can survive longer in team battles.
rabadon´s deathcap is of course for the ability power.
void staff is for magic pen.

when u are farming in mid, u play defensive. u try to hit the other char with command attack, and just keep on doing that.