Graves to me is a very good and mobile ADC. he has very high burst damage both in early and mid game. When he goes to the late game he will be a force to be reckon with as his items gets more damaging and his movement speed and attack speed will be extremely high so kiting will be very easy and will get you out of trouble.

Why i pick Barrier over ignite or cleanse is simple. This gives Graves the early game survivability and baiting potential that he needs. Having Barrier is better than ignite in my opinion is because Graves already has high burst in the early game but he has to get in close to do that damage. So Barrier will give him that extra health that he needs to do that burst and get out without trading 1 for 1 if it is a 1v1 fight.

Flash is pretty standard as it just gives Graves another escape spell as he can combo it with quickdraw to get out of sticky situations.