This will be a build for a lane Gangplank in competative play. I feel tankplank just fits more in today's metagame where tanky bruisers rule the scene. This build allows you to get right in the enemies faces without dying and still doing a pretty nice amount of damage.

A few notes on this build: this build will not work well for jungling. This will be aimed at the solo lane Gangplanks out there, as it does require quite alot of farm, which you just won't be able to get in the jungle.

Note: this is not an actual tank build. It's called tankplank because you're just alot more durable than the avarage glass-canon Gangplank.

Greater Mark of Desolation : By far the most useful mark for any Gangplank, allows for some great early game damage.
Greater Seal of Evasion : As we'll be going with Nimbleness, dodge runes are awesome. Also makes you that bit harder to kill early game and just makes you harder to kite than you already are.
Greater Glyph of Scaling Cooldown Reduction : More CDR equals more oranges! Along with every other spell which will now have a shorter cooldown. Win!
Greater Quintessence of Desolation : As more and more champions run armor runes/items these days, some more armor penetration can't hurt, right?

Pretty standard 21/9/0 mastery build, grabbing improved exhaust and max out Sorcery for even more oranges. Oranges are good. Also Nimbleness cos it's awesome.

Good:

Exhaust : Shut down them carries before you blow them up, added with your passive slow, people are not getting away from you.

Flash : As Gangplank has no escaping abilities, you want Flash. You already have amazing move speed so I feel this is a better choise over Ghost.

Ignite : Good pick if you don't like Exhaust. Probably even better in some situations. Adding to your already great damage, you'll be even scarier when they know your ignite is up. Also great to counter teams with alot of healing.

Viable:

Ghost : You could grab ghost and turn that good movement speed into amazing movement speed, but since we already have all those slowing abilities, do we really need more move speed?

Teleport : Can be a good pick in some situations, for example if you know you're up against a laner who can push really fast (Singed, Nidalee, etc) and you don't want your tower to die on your first trip back. Also good for dragon control in higher level play or even unexpected teleport ganks.

Bad:

You shouldn't really pick any other summoner spells, no other viable choises in my opinion.

As you'll most likely be in a solo lane as Gangplank, I'll cover the main itme build meant for solo laning.
You go into lane with a and a
You CAN start with 5x if you think it's really needed but usually the regrowth pendant is more than enough as far as early early game lane sustain goes, so I would recommend getting that.
Another viable, more agressive choise would be to just grab for the early Zeal/Trinity Force, but only do this if you know for sure you can completely dominate your lane without needing any sustainability items.

First trip back you should aim for a Philosopher's Stone, your or even your and a ward. (Really you always want to have at least one ward up covering your lane, cannot stress enough how important this is)
After that get your for some early game damage and start building a .
Alot of people probably disagree with getting a Warmog's so early on and will say you won't do any damage. However as I max my E first as tankplank, it already gives me some real nice early game damage combined with the Zeal. So grabbing an early Warmog's makes Gangplank an early game monster.

When you finished your Warmog's, start building the rest of your and get your as you'll have a pretty high health pool at this point, then finish up with an or a depending on enemy armor levels.

Other viable item choises include:

: Great item in combination with trinity force if enemy team is AP heavy.
: If you want to go more offensive, everything Gangplank wants in terms of stats on this item.
: For when the enemy team is THAT CC heavy, you don't have enough oranges. Alternatively just switch it up grabbing for tenacity and upgrade your philo stone into .
: Again only grab this if you simply don't have enough oranges to counter enemy CC. If you just want magic resist, I feel a Force of Nature is a stronger pick.

Passive: Gangplank's basic attacks apply a poison for 3 seconds that deals 4 - 21 magic damage per second and slows the target by 7%. This can be stacked up to 5 times.

Gangplank's passive, recently changed from a healing reduction to a stacking slowing effect on hit. This is an amazing passive and combined with your move speed and oranges, allows you to stick on a target untill it's dead.

Gangplank shoots a target unit for 20/45/70/95/120 plus 100% of his attack damage as physical damage. Gangplank gains 4/6/8/10/12 extra gold if Parrrley deals a killing blow. This ability can crit and applies on hit effects.

Your main poke/harasser. This ability is feared among squishys, target them with this in the late game and watch their health bar vanish. What makes this really good though, is the part where it applies on-hit effects, such as your passive slow, sheen, red buff slow, etc.

Consumes a large quantity of citrus fruit which clears any crowd control effects on him and heals him for 80/150/220/290/360 (+100% of ability power) health.

Oranges! Really though, a low CD Cleanse with a nice heal on top of it. Amazing ability.

Passive: Gangplank gains 8/10/12/14/16 Attack Damage and 3/4/5/6/7% Movement Speed.

Active: Gangplank fires his pistol into the air, disabling his passive boost but increasing his Attack Damage by 10/14/18/22/26 and Movement Speed by 7/9/11/13/15% and nearby allied champions' Attack Damage and Movement Speed by half that amount for 6 seconds.

I really love this ability. Passively increases your damage and movement speed, inreasing it even more when you activate it. Has a pretty large range so in teamfights you'll most likely affect your entire team when activating this.

Signals Gangplank's ship to fire upon an area for 8 seconds. Each cannonball deals 65/110/155 (+20% of ability power) damage and slows enemy units 25% for 1.25 seconds.

Gangplank's ultimate, very good if cast in the middle of a teamfight, slowing the entire enemy team. Also deals quite some damage to people standing in it. This also allows Gangplank to assist his teammates no matter how far away he is, can be a great life saver.

What I start out with completely depends on what the team decides to do at level 1 and also depends on who I'm going to be laning against. Generally I'll level up Parrrley first to make laning easier and for the extra gold when you succesfully last hit with it.
However if your team is going for a level 1 fight, I recommend grabbing Raise Morale first to give your team that early edge in the fight. Just wait before you put that first point in anything untill you're sure what you're going to do.

From there, rather than most builds, I will level up Raise Morale first. While Parrrley gives me some great early game harass/poke, I feel in this current meta with all the mean bruisers in that solo top lane, Raise Morale is a better choise as tankplank. It allows you to succesfully go toe-to-toe with most champions and actually beat them in a 1v1.

I grab my first point in Remove Scurvy at level 4, as that's when alot of junglers might want to try and gank you. This is again very situational and you might not even need to level it that early. In some cases you may even end up leveling it sooner and more if you're having trouble in your lane. Leveling this first does give you that extra sustain so if you really need it, it's not a bad choise.

I level Cannon Barrage at 6,11,16, like most ultimates.
I generally level Parrrley after Raise Morale, which means whenever you can't level up Raise Morale or Cannon Barrage, level up Parrrley.

If, however, you're forced to go to the bottom lane together with a support, it's probably better to level up Parrrley first, Remove Scurvy after that, with Raise Morale up last. Cannon Barrage whenever possible.

Early game:

So as this guide is aimed at the solo top lane tankplank, make sure you actually get that lane first. Bottom with a support works too but I feel he's much stronger up top.
Go to your lane with your regrowth pendant/health potion and try and farm as well as you can. You can harass your enemy with Q but I would advice against it. Rather save it for picking up last hits you would otherwise miss and save the mana to escape from a gank if needed.
Go back to base when you have enough gold to buy philo stone/boots and a ward , but try to push your lane up before you do go back.
In this early game you pretty much want to farm that top lane as well as possible. Make sure to keep wards up and look around on the map to see if anyone on your team needs some help from your ult.

Mid game:

You want to aim to get your Warmog's as soon as possible. Whenever you get it, you will start getting real strong. Having your E maxed at this point allows you to be able to 1v1 pretty much anyone. Meanwhile, keep farming up as much as possible to get Warmog's stacking and start building Trinity Force.
Generally the way you will behave in a teamfight, is wait untill the tank (or whoever else) engages the fight, position your ultimate, press E and charge in to get on that squishy. Exhaust the physical carry that's being the biggest threat if needed to help your team survive. If you're farmed well, you can even engage fights yourself at this point.
Don't get too brave though, you do have a ton of health, but you're still pretty squishy as you'll probably be low on armor/mres, so before you do engage, know what you're getting yourself into.

Late game:

When your build is completed, you should be an unstoppable force. Moving at the speed of light, blowing up squishies in seconds. Make sure to make every ultimate count and try and get to the right target as soon as possible in a fight. Still be cautious though, you may be tankplank, but you're definitely no Amumu. Be agressive, but be smart. It happens very often I see Warmog's Gangplanks rush into a fight and get blown up instantly, 3.5k health does not equal immortality, it merely gives you some more time to lay waste on the enemies. I know this sounds harsh but in fact those seconds make a world of difference, given the amount of damage you can dish out in those seconds.