This is a duel build for gangplank, one for Junglers and the other is for the Lane lovers.
Anything marked in red is bad, yellow is alright, green is good, and purple is questionable

Gangplank was born the son of the dread pirate captain Vincent the Shadow - one of the most wealthy and feared pirates in all of Blue Flame Island. One might think this would have spoiled the boy with a cushioned life of privilege, but the truth is quite the opposite. Growing up in the city of Bilgewater isn't easy; pirates are not known for their compassion, and that most certainly extends to their families. Vincent wanted his son to grow up tough and strong, so he was extremely hard on the young Gangplank. Even as a child, Gangplank was as mean as a snake and is said to have slept with his eyes open. As he grew, the young man rapidly became the most ruthless and feared pirate in all of Bilgewater, and his daddy was never more proud than on the day of his son's eighteenth birthday - when Gangplank stabbed his old man in the back and claimed the famed pirate ship, the Dead Pool, for his own.

The continent of Valoran, however, is a dangerous place for pirates; Gangplank could read the writing on the wall. The den of pirates known as Bilgewater would soon be pulled down by the undertow of Valoranian politics and the Institute of War. It was time for Bilgewater to have their own champion to represent them in the League of Legends, and who better than the fiercest pirate of them all? It is said that Gangplank has enough power and favor to claim the title of the Pirate King back home, but that he is simply biding his time and building his reputation as a champion before he returns to a life of piracy.

Yo ho, blow the man down. Or at least shoot him when his back is

PROS:
Great speed
Massive survivability
Huge damage output
Your a pirate

CONS:
Things with slowing % slow you more due to the higher speed
Squishy until you obtain the warmogs
The Parrrlay is hard to use for last hits, even though your suppose to

There are many builds for gangplank, there's "tankplank" "critplank" "ap plank" and many more, but i personally like tankplank with insane damage, therefore i go crit for the beginning and go tanky at the end, if i get the chance of course.

The reason for the two beginning items is simple for money and overall survivability, since the gold effect is now unique to that one item getting the avarice and the stone gives you a good advantage for this extremely pricey build.

You might of noticed the lack of boots. Well with gp i find them unnecessary with the two phantom dancers for speed and his E which gives him incredible speed with the active.

The last whisperer is for those pesky armor builders and tanks, helps crit a lot.

With the warmogs, you will be almost invincible, with extream hp regen.

Lastly the frozen mallet, this item stacks extremely well with the passive of gp. Together, the slow will reach up to 75% less movement speed. Stacked with your movement speed and the E active, there's no escaping gp. EX: Singed with his ulti on AND ghost still cant escape gp :]

The art of jungling is vary hard, Especially with gangplank. When i jungle with gangplank, i do the following: (remember to NOT wait for the parrrlay CD to kill some minions, in other words don't waste your time
1. Start out with a Cloth Armor and the 5 Health pots
2. Then Go kill the brown big wolf before the blue buff spawns, forget the two mini wolves for now (you can use a pot)
3. Go directly to blue buff, where you should get a "pull" where the mage in mid will take the aggro and run back to the lane. (use a pot or two)
4. Kill the mini wolves
5. Now if you are confident, kill the ghouls starting with the blue one, or you can go get the golems first (you can pot here)
6. Now kill the opposite of which you just killed, golems or ghouls, then go back to base
7. Obtain what you can, leaving gold for at least 2 pots
8. Now if you haven ganked already, do so if possible, if not kill red ( you can use a pot)
9. Now the rest is on your own choice, keep jungling, venture to theirs or gank

Since you are not Jungling your build AND your skills should be different.
What you should look out fore while laning with gangplank are as following:
1. ALWAYS last hit with your Q skill, Parrrlay if possible, but don't wait an unnecessary amount of time just to do so
2. Don't bother harassing with Parrrlay, its better used for the last hit on minions, just for the extra gold
3. Try not to use your E skill, Raise Morale unless there's a gank happening, or your trying to get back into your lane or anthers lane. Otherwise its a waste of mana
4. Try to heal with Remove Scurvy as much as possible, even though its about 80, that's still a lot
5, Getting first blood for gangplank is EXTREMELY helpfully, so that is always nice to get
6. If you have to go back to base, make sure your ulti is not on CD if the lane is pushed, kills minions fast
7. Have your teammates call for you ulti, don't put it out on your own
8. Solo laning is possible, i like it, whether its against one or two people

The Laning Masteries give focus on crit and pure damage output along with gold
The Laning runes give the following:
attack damage for all around
Armor pen for obvious reasons
Mana regen helps you constantly put out parrrlays

The Jungling Masteries focus on crit along with damage to minions and defense from minions
The Jungling runes are as following:
Attack damage for simply damage
Armor pen to kill minions faster

Flash is the most useful spell, it helps you engage, disengage, run past walls etc.

Smite is what you obviously use for jungling

Ignite works well with you passive and for the pesky Warwick or Fiddlesticks

Exhaust is sometimes god, works well with your passive but you can already catch up to people

Ghost helps but by the time you get enuf speed, you could a go out of there with flash easy-er

Cleanse is nice due to the double cleanse from Remove Scurvy but its not really needed at all

Rally is rally...no need at all

Clarity works on if you don't use mana regen runes

Heal works exceptionally well if used along with ignite, for a H&I surprise

Revive is only useful if you know your going to die

Teleport can be useful but i fine it worthless if you have speed to get to a lane

Clairvoyance is nice if your in solo que so you know when their mia, otherwise give it to the support