Gangplank looks weak but with the right guide and skills you can easily own with him.
For spells always take Flash and the second u may choose whatever u want mostly I choose ignite for the extra damage u can deal in early games.
For runes take crit and physical damage runes.
With Gp u need to take it easy a while don't try to act to be the hero when ur low level wait atleast until lvl 6 before u actually go in a fight. After u got ur ulti it is easy to own people in 1 vs 1 or in teamfights ur ulti is very handy.

ITems..
1 Buy a long sword and a health potion at the start.
2 Depending on the enemy u buy or ninja tabi or mercury treads.
3Finish Last whisper so u will deal more damage to tanks and other enemies.
4 Try to buy infinity edge for the damage and the critical chance to hit.
5 now U hit alot but u can use some extra speed and more crit chances so u will buy the phantom dancer.
6 For the touch of ur max damage u will the bloodthirster which u get some extra damage and lifesteal witch is handy in team and overall fights.
7 and last but not least u should have some armor. in the most games I go for guardian angel for some armor and magic resist but depending on enemy u can buy also thornmail at this stage.

Gangplank!!

I would say don't be to greedy early games with gangplank he isn't that strong early game. his first spell parreley and his second remove scurbvy will help u to get kills and survive. with parreley u are able to hit crits and at the late stage u will hit alot crits I maxed my hits to 993 with gangplank. Remove scurvy is so handy even if u got disabled on ur spells in teamfights by lets say garen u can still use remove scury and heal like 400/500 hp which helps u to survive. Raise morale will give u some extra damage and speed but when u activate it it can help u and ur teammates to get more damage in teamfights. U can also use raise morale with helping ur teammate with escaping using ur ulti and raise morale so your teammate can escape.
This month they have changed GP's ulti to a smaller area but more hits and it last longer.
Gp's ulti is really the cherry on the Pie. It can help ur friends outcuz u can cast it anywere u want. u can use it to save yourtower from minions and enemies at early games who will leave the tower whenever u use ur utli. And in teamfights it will slow the enemy for 25% who are in the area of the ulti so u have some advantages to.



Hope you guys liked my first build! sorry for bad english;p