Thank you:) Dont forget to vote;)

I agree with your build to a certain point. I dont reallt like madreds on Vayne, not the way I'm building her.
The reason is - madreds gives you a pretty decent dmg boost. However - lets say the opponent have 2000hp.
This is 80 dmg right? These 80 dmg cannot crit. And pretty much the whole concept on my build is critbased.
And the other think being - madreds is often used to kill "tanky dps" or "tanks"
Since the dmg from madreds is magicdmg, its safe to assume that they have decent magic resistance.
The only time I actually invest in madreds is;
1. If i have basically no magic dmg in the team (the enemy doesnt build mr)
2. If i also build a wits end(passive reduces mr) or even an malady(not on Vayne, pretty much only do this on warwick)

But, if it works for you, stick to it:)

Nice build, I like your thinking, I have done something similar, its listed in my third build Take a look

http://www.mobafire.com/league-of-legends/build/vayne-the-ultimate-chaser-84904

Random stuff? How do you figure?
IE, trinity and PD all gives alot of critchance. Since tumble is on a 2sec cooldown the trinity also proccs. This gives a massive burst dmg. Trinity+pd+grieves+BC gives massive AS.
It's basically AS/Crit but with the extra oompf from trinity procc.
In certain situations i go bloodthirster instead of BC, depending on the enemy team. With good AS you heal yourself pretty much with BT + 2xdorans.
And ofcourse the +100 dmg if farmed.

should i vote -1? nah, well see if you get high votes

i think your buying random stuff

You do that! Keep me posted on your victories;)

Looks good. Tested a similiar one before and it was good. Will definitely check it out.