Gangplank is a fun champion. His kit is comprised of a ranged AD nuke, an AoE team-based movement speed and attack damage buff, an AoE global damaging slow, and a self heal cleanse. His passive helps wrap everything up nicely by providing a stacking slow/dot that helps in chasing and jungling.

I've created two builds here and I will be giving explanations for choices of each.

(I've been up all night, so bear with me on grammar/spelling mistakes. I'll come through here and clean it up later.)

Build 1, Solo Top:

The tankier, the better. Often times you will be tanking creep waves when fighting the enemy. The flat armor/mr is there to help. The armor pen marks and quints are for devastating your opponent with a surprise 300 damage parley at a relatively low level.

Build 2, Duo Bot:

Shock and Awe tactic. You want to hit them hard from the get-go. CDR reduction allows for more parleys, while increased crit damage is...well...for increased crit damage. It's fun hitting your morale button, running from the brush, and critting the enemy for half their hp while they can do nothing about it. These runes are to give you an early game advantage, and then keep it throughout the entire phase.

Build 1, Solo Top:

Not much to say here. Standard AD carry build. Dipping into defense for some added tankiness and into support for death reduction, in case of a bad team fight or something. Improved exhaust, because you never know, that extra armor reduction might net you a kill.

Build 2, Duo Bot:

Standard AD build. Dipping into support tree for a little extra regen and faster leveling. Longer the buffs on GP, the better.

Build 1, Solo top:

You wanna build GP like a tanky dps up top. Philo/Hog is amazing and will help you survive strong duos/other strong solos. Avarice blade nets you even more gp/5 and gives you some nice early game crit for easy harass. Ghostblade is amazing on GP. Two seconds on an unguarded carry and they're toast. Also gives you some nice armor pen and cooldown reduction. IE will come quick if you farm as well as you should. Your gp/5 will help here. Phantom dancer is great. More movement speed for better positioning, more crit, and some much needed attack speed.

Your boots and last item are up to you. Frozen mallet for some added bulkiness, along with a wonderful slow. Or you can continue building glass cannon like and go with a tri-force. More movement speed, crit, sheen proc, and slow. Your boots depends on the enemy team. If it seems like they have too much cc for your oranges to handle then it's best to go with Merc's. If there are only a few stuns and you feel confident, go with lucidity.

Generally games will not go on long enough for you to get a full build, but if they do, you can sell the philosopher and HoG for a atma's impaler and a warmogs. If you chose to go the frozen mallet path you'll have a lot more HP than the enemy carries along with a lot of attack damage from your impaler.

SITUATIONAL ITEMS:

Executioner's calling. If you're facing an enemy with too much lane sutainbilty, pick up an executioner's calling. It gives you crit, life steal and an active that will allow you to destroy your opponent. Best for champions like Swain/WW/Udyr/Irelia/Mundo.

Build 2, Duo Bot:

Your job is to hit them hard and never stop. This can be incredibly easy, or incredibly hard, depending on your lane partner. Once you get to a decent level, 4 or so, you want to start harassing the squishies lane enemy. If you want to go all out, you can hit your raise morale before hand from the bush. They won't notice, and if they're far enough away from the tower they will take a parley or two and multiple auto attacks. If they're not in a position for a kill attempt, just harass with a parley every now and a again.

You're mostly praying for a crit. 10% chance isn't a high one, but when you crit, they're gonna know it. You want to get the cloak portion of IE early on to compliment your crit-harassment. Ghostblade to give you some slight mobility and easy attack speed, on top of cdr and armor pen. IE for higher crits, PD for faster and more frequent crits. Trinity force and bloodthirster to give you some (slight) survivability and loads more damage.

Build 1, Solo top:

QWQEQR
123456

After that you want to focus
R>Q>E>W

Build 2, Duo bot:

QEQWQR
123456

After that you want to focus
R>Q>E>W


Reason behind the W before the E on solo top is in case you make a mistake and find yourself stunned/slowed in a bad position.

Reason behind the E before the W on duo bot is because you want to be hitting the enemy hard early on. Morale helps more for damage.

Gangplank really only has a summoner's he should be taking.

SHOULD:
Flash - Do I need to explain? Good for chasing, running away, positioning in a team fight, face checks gone wrong, etc.

Exhaust - Helps A LOT in 1v1's and in case they have a fed carry or two.

Ghost - This isn't really needed due to GangPlank's E functioning like a ghost. Can still be taken over flash, though.

Ignite - If you find the enemy escaping too often, you might want to take this.

(NOTE: This guide is not finished, a WIP right now. I will be updating and cleaning up the next few days.)

Gangplank is a great duo laner, and can get fed quite easily with the right partner. He's a great asset to any team. His ult allows him to save lanes all the way across the map, while his E allows the team to run away from/catch up to opponent. Only a few examples, but I'm sure you can understands why he's a sought after pick.