First of all a carry must farm very well that means like 50 minions evry 10 minutes. This is your main obiective. Vayne is a very good mid champ so if u can go mid just go for it --> mid = more level + more minion farm.

You start with dorans blade then try to stay on lane and farm till u have enoght gold to buy second dorans blade + boots of speed. After u get your Infinity edge your dame will be awesome with your ulti activated. Then just keep folowing the build :p

Ghost and Exost are the best summoner Spells in my opinion because ghost works very well with your ulti and also for ganks you can get very fast on a lane to gank . Exost helps you to escape or to get an easy 1v1 vs an AD

Pros:
-Insane damege
-Stun/Stealth
- Good chaser
Cons:
-Kinda squishy if is not played safe
-Often focused