Hello, welcome, this is my first guide, and I've been playing Pantheon for a while now, I believe I am fairly good with him, but this guide is focused more for normal games and mid ELO ranked games...It is a good glass cannon build, Pantheon is a champion that works well against squishy champions, from level 1=14, depending on how fed you are, and sometimes, even till the end of the game.

As far as the build's concerned, it is focused around dealing a lot of damage, with the ability to absorb it, the sequence:
Boots -> 2x Doran's Blade -> Ionian Boots of Lucidity -> The Brutalizer -> Heart of Gold -> Trinity Force -> sell Doran's Blade and buy Black Cleaver -> turn The Brutalizer into Youmuu's Ghostblade -> sell Doran's Blade and buy Infinity Edge -> Sell Heart of Gold and buy Sunfire Aegis

VOILA :)

As far as runes go, I've decided to focus on armor and armor pen, since it is his focus, for he is

NOT

a

FIGHTER

.

Focused same as runes, but I recommend taking some in utility, for his mana hunger early on.

Khm, okay, shall we?

LEVELS 1-5:
play as aggressively as you can, especially if teamed up with a CC partner, if solo-top, poke a lot with the spear, and FARM A LOT.

Levels 6-12
You got your ult, start ganking, it is a good way to gain gold, plus you're helping out teammates, pushing turrets is necessary, start counter-jungling if you notice the enemy team has no jungler or if their jungler fails at key moments in the game.

Levels 13-end
This stage is considered mostly as free roam phase, as you spend no time at all in base, team fights are KEY indeed, the more you're involved in them, the more you contribute your team during the match, pushing turrets is key as well.