Welcome to my build to Gangplank , The Saltwater Scourge.
In this guide I will talk about some tactics and item builds on gankplank.

pros:
he is a pirate.
has nice movement speed.
build in heal and cleance.
huge damage output if you build critical chance and damage.
great farming potential.
his passive slows and does damage over time.
AOE ulti that allows you to help team mates and give a slight edge when both you and your laning "enemy" aren't there.
cons:
mana dependant early - mid game.
needs to get in melee range to do damage when Q is on cd , which is bad when squishy.
can't think of any.

I like to take Ignite and Exhaust when i know i can get the kill or a huge advantage in lane by using them right away at the first damage exchange ( to send him to base or get him low enough to be able to zone) .
However , when the enemy counterpicks you , you might want to go Ignite and Flash
because flash is a very important escape mechanism that might save your life more than once , i play safe most of the time , so i don't count on it.

I play him top .When playing gangplank , you need to remember that your Q Parrrley gives bonus cash.
Therefore I take an early point at lvl 2 , and max it 2nd since it is the source of the damage in my build. You can also use it to harass the enemy and if it gets crit , you can probably engage 1v1 and kill him successfully or zone him hard and keep Qing him and hope for an engage.Always watch your mana , since you really depend on it for the outcome of the battle.
Sight wards will keep you safe from genking.
Some of you might ask , why are you maxing remove scurvy first. well , that is because it gives a lot of health when used , and breaks any cc , so when you go 1v1 against the enemy , and use it , you gain a huge advantage (about 400 health).
When you are 6 , watch for your team ganks to help with ulti , that gives slow , and does damage. if not , you can use it to farm other lanes (if they are pushed to the tower or to push other lanes)
or the 3rd option , to save it for an all in attempt to kill the opponent.

When going into teamfight , always try to poke people with Q , hoping to make them retreat and give advantage to your team. Notice that in the damage build , if you crit the ad carry , the ap carry , or the support , you do about half hp !!!!