Gangplank is one of those champions that is forced to go tri force, ie and most of the time essence reaver regardless of the matchup. If you are having severe problems against AP champions you should buy hexdrinker before your tri force(first item).
Usually it is not a question of the build but a question of how you play this champion. You are given a cleanse in the form of your w so try to use it to get out of cc for example use it after amumu ults or after tahm kench eats you.
Ultimately you have to keep building full damage with your last item being MAW against heavy AP comps or randiums against ad comps(works well against yasuo).
To carry hard you need to build the damage however try to stay back in fights and let your scaling carry the game. The later the game goes the more game changing your ult and your barrels become.
Generally, Gangplank is one of the champions that is forced to go FULL AD, even if you're losing
Somewhat the only viable defense items for Gangplank are as follows :
Maw of Malmortius / Dead Man's Plate / Sterak's Gage
Usually it is not a question of the build but a question of how you play this champion. You are given a cleanse in the form of your w so try to use it to get out of cc for example use it after amumu ults or after tahm kench eats you.
Ultimately you have to keep building full damage with your last item being MAW against heavy AP comps or randiums against ad comps(works well against yasuo).
To carry hard you need to build the damage however try to stay back in fights and let your scaling carry the game. The later the game goes the more game changing your ult and your barrels become.
Feel free to pm me any questions!