My Personal Vayne Guide / Build
Vayne Bot / Top, you choose. 
I personally run Flash+Ignite, I'm not a fan of Cleanse, so come at me and insult me, I don't care, ignite provides a better kill potential for early game, being able to get gold and finish my core items. Also my build will have Banshees in it so.
My Build
Start - Boots + 3 Pots.
3 Paths -
-If you manage to die before getting 1450 Gold, then get Short Sword / Vamp Scepter, eventually get a BT.
-If you're versing a tanky adc (Graves, Urgot, etc), Zeals to proc your W faster - Then focus on your BT.
-If you manage to gain 1450 Gold, get BF sword - Get Vamp Scepter, then BT.
Next, get Phantom Dancer - First, get Zeals, then the dagger, then the crit cloak.
After that, it's all situational, you either want to get yourself more damage, and go for Infinity Edge, or build a bit defensive, and go for Banshees.
If you got banshees first, get an IE.
If you got your IE first, get banshees.
You'll probably be around 25-35 minutes, with all those 5 items required; That's IF, you farmed well.
Now, situational - If you find yourself dying a lot, get yourself a GA.
~ If they never focus you, and focus your initator, get another Infinity Edge or SoTD to deal max damage.
~ If your enemy has a lot of armor pen + magic pen and usually start focusing you, just get Warmogs, the s3 Warmogs is really good and unless you're playing blinds, only another Vayne would counter you with Warmogs.
If you want, sell your boots, and buy something else that you'd think would make you stronger.
CS time -
5:00 as much as you can.
10:00 as much as you can.
15:00 - 50-100.
20:00 - 80-120+
25:00 - 125-150+ (You're going to be in a lot of teamfights and get objectives, so)
30:00 - 175-200+ (You'd like as much farm as you can, because this is heading into late game, if you haven't gotten your Banshees, and they're smart enough to focus you, then you're probably stuffed.)
Who to focus -
You can ult+tumble and run to their adc, and kill them, as long as they're close to you.
Kill the bruiser / assassin who's diving, trying to kill you, just Ult+Q away, then aa, assuming your teams going to be hitting him.
Kill the one that's dealing the most damage.
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Downvote it, Upvote it, I don't care, this was mainly to show you my build for Vayne, criticism is allowed, but don't go to far. 
Thanks.
P.S I know I typically just gave a guide out, but I don't really care.
Feedback is appreciated, thanks. 