Alright, so I'm gonna make this short but sweet. Firstly playing with Vayne, rolling is a key concept that you'll need to master in order to use her properly. Mouse position being the key part of this.
The build listed above is dependent on whom you are against. You may need to switch items as you see fit, if your against tanks that are focusing you, you may want to consider getting madreds for the armor before getting mallet.
So here's the order
Dorans blade -> Zeal-> Ionian boots ->(depending on the situation) Blood Thirster -> Mallet -> frozen Mallet -> Phantom Dancer -> (if you haven't gotten it already) Madreds blood Razor -> banshee's veil. Depending on how the games going you may want to consider getting your self either a black Cleaver, if being focused a lot switch to a Guardian Angels, if they have a lot of armor get a Last Whisper.