Gangplank is one of the most interesting champions in the game in my opinion. One thing that makes him so unique, is that with this build I have been 3/9 and still been able to complete my build by 30 minutes...of which I ended the game 15/10. If you are able to keep an eye on the map early game to help pick up a few assists or kills with your ult the game will be done fairly fast.

For runes I prefer armor penetration marks, mana regen per 5 per lv seals, cdr per lv glyphs, two crit damage quitessences, and one movement speed quint.

Armor penetration is huge for gangplank. You find that most people start building armor of some sort when they realize you are hitting them for close to half their health, and thus the armor penetration is very critical.

The mana runes are a must for gangplank because he is the most mana hungry champ I have come across so far, especially early game.

The cool down runes are fairly self explanatory. His main source of damage is parlay, and cannon barrage of which are limited by cool-downs.

For Quintessences I chose to use 2 quints of furor, or crit damage, and one quintessence of swiftness. The crit damage is obvious, GP builds off of crits, however I believe the rune of swiftness is extremely vital. This is a rune that I swear by and use for every single of my rune pages. It is often the difference between either getting away with 20 health, or barely getting off that last shot before the turret for a kill. It gives you that little bit of movement speed that allows you to either run away or chase a little bit better. Late game this combined with boots of swiftness (my preferred choice of boots for GP) and phantom dancer allows you to run into a group of enemy champs, pop your parrrley on a caster with less than 50% health to pick up a kill, and run away unharmed.

For masteries I went the standard 21/0/9. All of the points I have allocated into the offence masteries are important where they are with the exception of the minion damage. If desired you could switch them to increase your attack speed, it is simply a matter of preference.

For the 9 utility points, the 4 points into experience are very important. GP leaves the lane a ton early game, either to gank (which isn't recommended because of his lack of cc or damage early because of poor crit strike) or to go back to buy avarice blades. The final point is up to your own discretion. Putting it either into the gold per 10 or the 15% increased neutral monster buff duration is once again completely up to your own preference. I just think the gold per 10 fits nicely with the avarice blades, because it puts you at 16 gold every 10 seconds, which is 96 gold every minute. that means that in 10 minutes after standing still, not farming at all, or helping get kills you can buy a BF sword...not counting the amount of gold you normally receive automatically.

Many people would consider getting 3 avarice blades as spamming and it not really being a build. Getting 3 blades makes all the difference in the world. As soon as I get gold in the lane phase I go back and grab avarice blades. Somewhere in there I do grab boots of speed, sometimes it's after completing my first blade, sometimes it's after completing all 3. It just depends on the game and how much gold you have when you go back. For boots I prefer boots of swiftness because if the ability to get in and out quickly to use parrrley, but if there is a bunch of cc on the other team I would recommend mercury's treads.

EDIT: I would actually recommend building Executioners calling, then once you complete the rest of your build sell it and buy the Bloodthirster at the very end. This allows you to get your higher lifesteal quicker and money into phantom dancer.

After building infinity edge there are two options for life steal. Executioner's calling, or Bloodthirster. Executioner's calling does give you 15% more crit, but with IE being buffed for an additional 5% crit, 75% is high enough, and the extra 75 damage and 7% lifesteal are worth the lost crit strike. If you go for bloodthirster don't complete it until you build your phantom dancer.

GP is so fast at getting gold it's not worth selling your avarice blade until you can straight up buy Phantom dancer. After that, go ahead and complete your thirster if that's what you chose to get.

Last Whisper is a must for GP. Most champs will have started building some sort of armor, especially tanks so being able to cut through it makes him great at ripping down tanks as well as mele carries that decided to get some armor to combat your damage burst.

I can't count the # of games where I have had 4-5k gold with nothing to spend it on. When you die, and yes it will happen, or when you get a chance to go back

My preferred choice for spells are Ghost and Exhaust. There are many times where I will be farming/pushing a lane while my team pushes another area. Between all of my speed boosts, my ult to slow the other team, and ghost I am able to get to a team fight extremely quickly when needed.

I know many people use ignite with GP instead of Exhaust. From my experience the champs that rip Gangplank down are the other ad carries, which are often ranged. Exhaust is important because you can get one parrrley off, sure it drops half their health in most cases, but by the time you reach them their life steal has gotten them most of their health back, and it's now too late for you. Plus ignite is virtually useless after lv 5, because you now have your ult and can pick up those few kills that need ignite with your ult.

Farming for GP is VERY easy. By mid game he is critting so often that you just click on one minion and you watch him run around and kill the entire minion wave in 6 hits. The most vital thing for his farming though is to use parrrley to get minion kills. 16 additional gold when maxed out is a ton of gold, especially if you can get 2 minion kills with parley in a wave, and kill the other 4 with auto attack. Often I will walk past blue or red, even if I'm too low to grab them (aka don't have lifesteal...on a side note don't grab red or blue if you are about to recall...you don't have the skills to increase the length of the buff so don't waste it, even if it means a team-mate grabs them instead of you) and kill the neutral monsters just to get that extra gold.

Gangplank is an absolute beast of a champ and is a great addition to any team. It doesn't matter where he is, it's possible to help a team fight with his ult. If your doing bad, don't worry he's the best champ in the game to turn things around because of his farming skills and gold intake. As a final note, I can't stress how important it is to get the quintessence of swiftness! Have fun, and I hope you can enjoy Gankplank as much as I do!