This is a guide for a pro Gangplank.
I don't know how to do any fancy things that I'm sure most of you vote on, I just enjoy GP.
And this is a build that works for me and thought I'd share it. I'd like to get good reviews. But if not that's fine, at least I tried. Hope you guys enjoy, thank you.

For masteries I do 21-0-9 getting cool down and attack speed. And then mana regen for early game harassing and to lane longer.

For runes I get armor pen marks, attack speed seals and gylphs for a quick boost in the start. And crit percent quints.

Start with Brawler's Gloves for the extra crit and harassing. Grab mana and health potion to lane. Then grab zeal, and another zeal because they are cheap, and its good crit, movement, and attack speed at the start. Next up is boots, now you get Boots Of Speed then the finishing boot is depending on the team you're against. Merc for CC like Blitz, Sion, Alistar, anyone like that. Or Tabi if you're against high AD champs. You get the idea, boots arent a big need for GP he has a skill that is like Cleanse and a skill that increases attack speed and movement speed so it doesn't really matter to much. Then get Infin edge, get cloak of agility, then BF and just finish it off. Cloak first because of the crit and Raise Morale should be high enough to give a little extra attack bonus that BF doesn't need to be rushed. Then you finish off your Phantom Dancers for more crit, attack speed, and movement speed. And for the last two items I like to get Blood Thirsters just because that damage and life steal is amazing. And you will be hitting 1.3k crits with your Parrrrley. And around 900 crits normal hit, and your crit rate will be at about 90% so pretty much every hit. And the life steal on top, you wont die.

For skills, get Parrrley for harassing and damage, plus gettign last hit on minons is a good money boost. Then Raise Morale for quicker pushing and if you are trying to run to catch up to or run from enemy champions. Then get Remove Scurvy at level 3 just to be safe, if you get ganked and get stunned by Veigars stupid AoE stun, you'll be safe, no CC will stop you and you should be able to get to your turret pretty much untouched. Then max out Parrrley ASAP. And level up Remove Scurvy maybe one more time, then finish Raise Morale. And finish off Remove Scurvy at level 18.

Get Ghost, for getting across the map, running to enemy champ, from an enemy champ, to get to team fights, etc.
Get Exhaust. It's helpful, totally slows people down, and gives GP just enough time to smash them.

Pros:
[*] Quick killer
[*] High damage
[*] Extremely fun to play
[*] Good ulti
[*] Has a heal and passive movement speed and damage increase.
[*] I could go on forever about how pro GP is

Cons:
[*] Gets raped if focused. (but who doesn't?)
[*] I can't think of anything else

So for 5's. Get mid. Harass whoever you're against. Hit them whenever your Parrrley is off cooldown. You'll crit some times and it will mess them up and send them back and you'll get to feed on mobs (nom nom nom). Pay attention to the map at ALL TIMES. You can't rely on your team if you see someone missing, be cautious. If they are pushing on top or bottom, run up (use Ghost) and help get kills more than likely you will get a kill or two. Don't waste your ulti, look at enemy champs, if they're running back to tower they are most likely hurt pretty bad and use your ulti on the tower, boom, free kill. Now, don't waste your ulti on one champ if they are at full hp, use it only on team fights, to slow champions from getting to you or a hurt team mate, to slow them from running from you and your team, and if they are all missing use it on Baron and catch them getting the buff and run in for the gank. On towers, go with people like Tryn, or Yi, or Jax, someone with attack speed and damage and use Raise Morale, the tower will be gone in no time. Use Raise Morale to help hurt teammates get away, or to help your team chase enemy champions that are caught in your ulti.

If you are in a lane with no one against you, use Parrrley on mobs to last shot them for that extra 10 gold or so. Once you get the last two Phatoms and a BF Sword for your Blood Thirster youll be one shoting mobs making a ton of money quickly.

As GP my recent games have been:

16-4-11 Victory
06-0-05 Victory
08-4-10 Victory
06-2-06 Victory
11-3-07 Victory
05-0-02 Victory
08-0-03 Victory

Half of which I didn't even finish my build on, would get 2 zeal, my boots, and like a BF and cloak of agility and it'd be over.
GP can dominate in 3v3, and do amazing in 5v5.

Thanks again guys for looking at build, it was my first build I've made and i hope you aren't to harsh in your comments but I do enjoy feedback. And go kick some *** as Gangplank. Thanks :)