incase anyone wants it, this is what I do for my GP.
21/0/9 Masteries
Attack Speed quints, crit chance reds, armor yellows, and CDR blues
Flash + Exhaust (usually)
for skills I put 1 point in parrrley and then max out E and W as fast as possible with E first. I also put a point in R evey time I can.
I like to build the following:
Madreds Razor -> Wriggles Lantern
Boots -> Zerker Boots
Avarice Blade -> Ghostblade (last item)
Giants Belt -> ruby -> Regrowth Pendant -> Warmogs
Chain vest -> Atmas Impaler
Negatron Cloak -> Banshee Veil (if they have AP casters that are focusing me)
OR
Zeal -> Tri force (if they are more AD based but usually go with the Veil)
I end up with like 190 armor, 120 MR, 4.2K hitpoints for defense. Plus a self heal and cleanse with Remove Scurvy. Plenty of lifesteal as well with wriggles and the damage output. I also have around 430 move speed with his E passive. Plus blocking 1 ability effect every 45 seconds is nice with the veil. His W will heal him for 360+ per.
For offense I end up with 1.4 attack speed, 280ish AD (with his E passive), and 50% crit chance. Hitting his E for the active effect makes his move speed jump to 480ish and AD over 300.
Basically he's a monster to take down even in team fights once built this way. Very tank, hard to focus, and can escape CC. It's funny watching a whole team blow all their CC cooldowns on me at the start of a team fight to which I eat it off, back up a second while my team goes in to start dishing damage and then I come in a second later and seal the deal. There is no running from a gangplank, especially if I have a red buff. Ult + Passive + red buff and if I get Tri force even that all can stack to practically stop people in their tracks.
The reasons for my summoner abilities are two fold. Flash is great for getting to and away from opponents who use the same ability. Exhaust I keep because it helps with slows if my ult is down or they flash through it before I can apply another slow of a different sort. Also, about the only hero that can takedown GP is a well built trynd. GP can take his initial life down to zero FIRST, but then you are stuck with an endless raging trynd beating on your butt and not dying. It's not hard to kill a trynd, but you need exhaust to do so if they are good. Exhaust him as he starts on you, then blow him up to make him waste his ult. When he comes for you then run. Watch him blow his mocking shout for a slow and then use remove scurvy to stop it. At this point you should be able to kite him until the ult wears off and he then will die.