This build is based off of Chineseflame's build which works very well but I wanted to make a few changes which I think work slightly better. For any of the ideas borrowed from his guide I give him full credit. Hope you guys enjoy, please leave feedback in the comments.

Pros:

Insane damage on parrrley, applies on hit effects and can crit
Has a cleanse and heal as a skill
Denying experience with raise morale early game cripples your laning opponent significantly
Cannon barrage is great for finishing off enemies and for team fight damage and slow
Can poke in and out with parrrley

Cons:

Generally mana starved but the meki pendant as a starting item and mana regen seals help a lot
Squishy
Easily killed if remove scurvy is on cooldown
No CC besides ult

Greater Mark of Desolationx9 Armor pen offers the most benefit throughout the entire game. Refer to http://www.mobafire.com/league-of-legends/build/rune-tips-what-secondary-and-primary-means-and-more-24255 for more information.
x9 These help immensely with Gangplank's limited mana pool to be able to spam Parrrley and it helps with denying early game.
x9 These along with , , and masteries will bring us near the 40% cooldown reduction cap allowing us maximum usage of our skills and increases dps by allowing parrrley to be spammed more.
Greater Quintessence of Desolationx3 Same as marks.

Typical offensive masteries with improved ghost, extra exp to further the gap between you and your laning opponent, and extra regen. and are crucial to maximizing our damage output on

For summoner spells I go with and for increased survivability and chasing. is useless since we already have a cleanse in . I prefer ghost and flash over or since ghost and flash provide both defensive and offensive uses.

Pretty straightforward, starting out at level 1 with for denying. Then with one rank of at level 4. Pick up the ult at 6. Continue with prioritizing R>Q>W>E.

After experimenting with many starting items I settled on the which is strange because it doesn't build into anything later on in the build. The 390g spent here allows you to start out with 2 and sustain your usage of for denying as well as have enough mana for . This is critical because when denying, the enemy minion waves are always a lot stronger than yours and pushing up to your tower. Having enough mana for helps with last hitting and preventing too much tower damage. Without a denying leaves you with no mana to or which allows your opponent to have their way with you as you have no way to heal up or harrass. Trust me the will pay off. Its only 390g and will sustain your mana needs for the whole game until you sell it in late game when you dont need the extra mana regen. Having mana for also lets you get more last hits and get the extra gold from last hitting with it which helps cover the cost of the 390g not put towards the main items in the build.

Try to save up 2550g before your first trip back which allows you to grab 2 which give you 24% crit chance as well as 1 gold a second which is important in funding the next few items. 1 gold a second translates to 600g every 10 minutes which is like an extra kill every 5 minutes. If you managed to save up 2550g you will also be able to grab which will give you some nice cdr for your abilities. As gangplank you should be darting in and out of battle with parrrley so and aren't as useful as they are on other champions. Remove Scury also makes redundant.

Next we will start building our starting with the . After the completion of you should be hitting huge crits and with this chunk of attack damage the becomes very beneficial, doubling the damage of . Grab this then pick up some much needed life steal and more crit chance from an . Next build one of your into a which provides all the stats we need: damage, crit chance, armor pen, cdr, and a chasing/escaping ability. Finally build the into a

After the if the game is still not over, the last item is completely dependent on the enemy team comp. Selling an you can go for a which will cap out our crit chance and give us more survivability with an insane move speed. If you are having trouble with the enemy tank, a is a good choice.

Denying works best mid so try to call for mid in the champion selection screen. Start off by waiting near the nexus for the minions to spawn and when they do kill one of the melee minions and proceed to the middle. By the time you get to your tower raise morale should be up again and you can kill another melee minion. Continue denying melee minions and cannon minions when they come as they provide the most experience. Work on last hitting with your attack and parrrley. Harrass the enemy champion if you have mana to spare. You should be backed against your tower so you shouldn't have to worry about being ganked.

Once you hit level six continuously check on the other lanes for opportunities to use your ult to assist in a kill or even earn yourself a kill. You can also use your ult on the enemy wraith camp to further increase the level difference between you and your laning opponent.

Thanks for reading, hope this build works out for you. Once again credit to Chineseflame for inspiring me to make this guide and any ideas I borrowed from him. Leave feedback in the comments!