Here is my favourit build with GP, he is so much fun to play ! :D
If you play him right, you can gank very easily, and become the sickest carry :O

Start of as shown, and follow the guide until you got full build, then you have to sell your Wriggle's to one of the items i listet up in the end of the build, its situtional, so just pay attention till, who do you get dmg from? who cant you dmg etc.

Jungle without help:
- start wolves
- Wraits <-- USE smite one the big one!
- golems
- go back and buy armor and one HP pot
- take the rest or gank

Jungle with help:
- start blue
- wolves
- wraits
- back or take golems if you can, and then back afterwards..
- buy armor and go take the rest and gank :)

Here it is very simple, if you team aren't ******s, and dont have feeded mordekaiser, cho etc. you need to do following:
- open up with ulti
- use e
- AND SPAM Q - Q - Q - Q
- now you have gotten you pentakill cause of your insane dmg + survivabuility ;)
OPS! if Malz ults you, dont be scared, just eat some orange and you will be just fine :D