Hi Mobafire, my name is Viperoux, and this is my Gangplank build!
Ever since I started playing, I've been fascinated with the Saltwater Scourge, namely Gangplank.
He has an amazing W ability, which allows him to stay in lane for nearly the entire early game. His Q is my favorite, it's poke ability is just amazing, especially in the early game - it is however not useless in late game, quite the opposite, it has an amazing damage output, and if you get lucky with a crit, you can easily take down single targets. I play Gangplank as a solo top character, mainly focusing on crit and health items.

I handpicked these runes to maximize the efficiency in both the early and late game. They gives you a considerable amount of cooldown reduction, a great deal of armor penetration, allowing you to pick up a few more easy kills. The crit runes may seem weird, but they do actually give you an extra boost, and the burst damage from your Q when you critical strike is just spectacular.

These are my standard 21-9-0 damage output masteries, I decided to go tanky so that I am not as squishy late game. (For those of you who don't know already, Gangplank gets really squishy later on if you don't buy tanky items.)

These items I picked to give you a great deal of damage output and sustain at the same time. Personally, I love hitting those crit Parrrleys, hence the crit items, however I hate dying alot later on, after having a good start of a game, so I go abit tanky later. Atma's Impaler suits Gangplank excellently well, especially in combination with Warmog's Armor, definately a combination I would recommend in any game mode for the Pirate!

Start by maxing out your Q (Parrrley), it has an amazing damage output throughout the entire game, and you ought to prioritize it, always! Next up is Remove Scurvy, it's one of my favorite abilities, since it removes all CC effects on your character, and heals you for a great deal of health! Gangplanks E ability, I rarely use when I go alone, you will mostly use it in teamfights and when taking down a turret or a large minion/baron nashor/dragon. You tick your Ultimate (Cannon Barrage) at level 6, 11 and 16 as usual.

Heal and Exhaust always seem to work for me, Heal is great when you are out of mana, or when your W ability is on cd. Exhaust is a must for catching up with enemies, and landing your Q, it's likely to result in a few extra kills that you otherwise would not have gotten.

Pros:

Able to stay in lane longer than nearly any other champion.
Great potential both solo and in teamfights.
His Q ability is one of the few abilities that can crit, if not the only one.
He has good utility and relatively low cooldowns.
Great farming potential.
His passive (Grog Soaked Blade) can, if you are lucky get your several kills that are out of your range, this Passive also applies to your Q (Parrrley).

Cons:

Can be squishy early game, but hopefully not with the right gameplay and items.
Is able to run out of mana fairly quickly, so if a teamfight is imminent, try to save your abilities.
His Ultimate (Cannon Barrage) can miss the target completely if unlucky.
He is so damn pro that you might get accused of cheating when owning people! D:

Gangplank isn't the best in team fights, there are however a few things to consider when playing him. His Ultimate is global, meaning you can land it anywhere on the map, even in the Fog of War, do note that your ultimate slows everyone (enemy) in the area when active, so it can be used to save teammates that are far beyond your reach.
Other than that, his E ability is great in teamfights, boosting everyone's movement and attack speed, great support ability.

Lastly, for farming, you should know that last hitting a minion with Gangplanks Q ability (Parrrley) gives your up to 8 extra gold when maxed. This is excellent when farming, and is useful in particular in the early game, so try to last hit atleast a few minions here and there with this ability.