This stuff is a really cool stuff that I have play a lot of times.
Build tankiness on graves will permit you to deal a lot of damage during team fight, and also to keep you alive. This build make graves super effectif ! You will get an ADC with more than 3500hp, 400ad, and a lot of armor penetration ! You will be a big problem for the enemy team cause of your AoE damage.
Lanning phase should be normaly easy against most of the matchup. Just try to put pression on your enemy and to keep an eyes on ganks from the enemy jungle before your level 6. When you will be level6, you will have a good escape with the R and E that permit you to dash twice. You can even turn a gank on a double kill if the enemy top layer was low life.
You gonna build at first Youmuu for get armor pen. (which is good against all your matchup) and also get escape if you want to split push top tower.
Now the most interesting item of this build : the Frozen Mallet. This items is really effectif on Graves ! That will give you 650 hp, 40ad, and a really good passif ! The Frozen Mallet passif will permit you to escape from most of the situation ! Each time u will shoot an enemy champ, he will slow, and that permit you to kite him and reload your 2 bullets.
Malmotus and Sterak build then for avoid enemy burst of assassin champs.
Then a death dance as last items for get sustain and avoid burst as well.
During team fight, don't hesitate to jump in for try to kill an enemy in a bad situation. If you have in your team a Morgana that can put a cage on one of the enemy carries, try simply dash in with your E, use smoke on the rest of their team, then A and R the carry cage by Morgana, normaly u will be able to one shot him (or put him very low life).