This is my first (and possibly last, I dunno) build on Mobafire, and as the title says, it's HORRIBLE because I use a mix of Tier 2 and 3 runes, being too lazy to buy Tier 3s, so the runes here are what it should be. As GP is a really easy champion and you've probably read the top builds of him, you already know most of what I'll be saying.

This build will be focused on solo top and jungling. And possibly supporting if I feel like it.

Enjoy...

For items, I start with Cloth Armor and 5 hp potions and turn Cloth Armor into Madred's Razors as quick as possible. After that I buy Boots of Speed and rush for Sheen. If the enemy has a lot of CC or AP users (usually they do), get Mercury's Threads, if not, I prefer Berserkers' Greaves. If the enemy deals more damage than you've expected, you should buy a Giant's Belt. If you think you can reverse the damage via lifesteal, go ahead and buy a B.F. Sword. If you feel that you want more speed, build Phantom Dancer right after Infinity Edge, then Warmog's and don't buy Atma's.

Pretty simple and short.

Also, if you're trying the jungle route, please do it on custom first. I've had quite a lot of deaths while perfecting it for my taste.

As summoner spells and runes are the only thing I dislike in this game, I only take:
Cleanse to remove Ignite and Exhaust;
Flash to catch up to Flash users;
Ghost to catch up to Flash/Ghost users;
Teleport to get back into your lane faster;
Exhaust to make all those Tryndamere players QQ.

As this build is... "unique", you can use it for jungling, just replace Cleanse with Smite. Heal when needed with health potions.
Start off by killing the big wolf at the wolf camp (try to get the last hit with Q) and get someone to pull the Blue Buff (Golem), when you get hit, use a health potion, and smite the Golem at ~450 hp. Kill the Blue Golem camp -> wolf camp ->

~40 second gap between Smite uses. (use the time to gank mid or top (FIRST BLOOD) OR get into position to kill the wraiths)

-> kill the Wraith camp (kill the big Blue Wraith with Smite first) -> kill the 2 mini Golems -> kill Red Buff (golem) and the rest of the camp. Heal up with a potion if you have any left, eat an orange to be ok and check the lanes for possible ganks (I usually go back if top needs help, because I'd rather get another item before running out there).

For the jungle route, I do not take Phantom Dancer.

GP is a GREAT solo top farmer. If you are good at mana management, you can both defend yourself from the enemy AND use Q to farm up some gold between auto attacks. Smartcasting with shift help a lot.

The gold bonus may not feel much at the beginning, but when it becomes +8 gold per creep, you try to do it every time you can.

Also, if you see that an ally is coming in for a gank, do not change your play style. If you've played aggressively, keep on the aggro with Q, if defensively, keep it up right until the ally enters the bush nearby and release hell on the enemy (usually E -> Q -> aa (auto attack) -> aa -> Q -> aa -> aa)

If you are still reading this, that means you may have liked (OR HATED) the guide.
Thanks for reading.