This build is quite the fun build to play.

It messes with the opponent and you are quite strong.
Keep in mind that the usual routine is Powerchord Q -> autoattack -> E -> W -> Powerchord Q
I usualy don't have wards in the bush but to use them is no mistake, however if you can get an enemy to dive you, use your ultimate and Powerchord E to kill them under the turret.

The best time to fight is right after you get the high dmg boosts from.
Rabadon
Seraph's Embrace

Also don't forget to harass alot when you have your lich bane.
If fighting a high HP target don't hesitate to chip away at it's health, with the lich bane this will ensure him to get back.
If fighting someone you can't do much dmg to don't hesitate to gank with your ultimate.

Don't forget to sell your boots at the end if you've gotten the void staff and don't need the magic pen anymore.

Most fun is had when you're besieging the opponent with your team while unkillable due to heals and dealing TONS OF DAMAGE with lich bane + powerchord

Have fun and leave a comment so I can improve the build
(still looking to do an AD sona build :D )