Hello, since graves came i only played him, so i have a bit of experience by now.
i mostly play support/ ap so im not that familiar with carry, but im sure this build is what you need!

Graves is a ranged who as basiccly only 1 ability that does dmg(your w isnt a dmg dealer) and your ulti, when 16 your only gonna use it no so often cuz your auto attacks are much more powerfull

I play graves as a mid player(unless theres a tanky/support who gives away kills in bot lane)
Because of your short range mid is the best cuz is a small lane
you cant solo all to good cuz when you miss your E your dead, unless you flash +W+E+exhaust -_-
but when mid you need to harras allot! and that means dont run after casting your E just auto-attack it will make them cry.

Pros
-good farmer
-can pretty good gank when using spells right
-can chase with your W and E
-nice carry when placed well
-Good Aoe
-Has a big shotgun! (beat that ashe:) )

Cons
-aimed allot in tf
-short range Q(get closer with your E)
-squishy when ganked and out of combat
-can get ks allot in begin =s
-not that good ulti

You ofc need only 1 carry in the team so when playing draft pick or ranked, discuss with your team whats best, if the enemy team got allot of AD, then its good because you stacked up some armor!
when your team is fully AD, you might take another champ cuz when the enemy team got armor its basiccly GG for the enemy team

Runes, not gonna say to much

stack armor, Magic resist and armor pen
dont need more

21-9-0
same for every carry

KK items, next things you need to know about items!
2x dorans blade for health(your squishy!) , ad and lifesteal good start
next get Besrekers graves, more AS for harras and farming
getting zeal next is so gooooood, movement speed= quick ganking and its cheap later you can build it into phantom dancer, next is bloodthister, if your unfed you can sell a dorans blad now
Bloodthister is a very good start(100ad when stacked) so farm minions is really needed( go jungle when you have time) after that get you infinity edge! this will break the every champ! with the zeal you got early you have some crit and that gooood you can sell all your dorans blade now, IE is very expensive, next phantomdancer shouldt be a problem cuz its only 1630 a upgraded zeal is always good! this is your core build
Besreakers graves
Bloodthister
Infinity edge
Phantom Dancer

Next is late game
trinity force to make you unstoppable and frozen mallet to stop them!
you can awalys go for antother phantom dancer or Armor pen. when the enemy team is doing nasty

i dont know if you can jungle with graves, maybe his passive can help him?

Get Q first for the dmg ofc, then smoke for farming and closing of the supports or skillshot champs(lux morgana nidalee etc..) you can build you E quicker for better harrs with auto attack

His passive: always keep this up!, this will make him less squishy let more harras in and so they aint got no mana more then BAM (first blood = feeded :o)

His Q: your basic harrasing ability, level this up first for better harras, after late game this aint be doing much dmg any more( only 400)

His W: first ability to tosh in when gank, slows them AND they cant see were youre going, lvl this up second

His E: nice ability for a carry! as and wall jumping + good chasing, need more?

His ulti: well im dont think his ulti is a killing blow, more for aoe fights and finnishing offs, i almost never use my ulti and late game :o simply i auto attack much harder

Flash always have this! always! always!always!always!always!always!always!
exhaust good for melee champs to hold down(when build in masterie) and slows down

ignite is a meh, exhaust is much more efficient

^
the rest you should consider youself but these | are the best

Hope you like it and and helped, this is my build and if you got a better idea, plz tell me or make your own!

im not pro graves but i can play with high elo players