2010-12-13 build changes:

Fixed masteries to 1/16/13
Why I go with these masteries is because of the needed mana regen instead of dodge.

Fixed item build for more effect in damage early on so you can keep up the rate with damage + survival even better :)

More detailed build and masteries explanation.

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Detailed build coming in any day soon now.

Boots kind of depend on opposing team, but i usually go with mercurys treads or boots of swiftness. Start with dorans blade and go mid or go lane with someone like garen/taric/sion/olaf/xin or such. You'll start with around 780 hp which is very high for a damage dealing champion.

Masteries: 1/16/13

Because of instead of going 21/0/9 like everyone usually does with pantheon I take whatever is necessary, Like exhaust upgrade, ghost speed mana regen, longer buff duration, more hp, more defense and so on.

Exhaust for first blood and catching up later on, exhaust replaced ignite.
Ghost for speed and catching up to stun/spear.
Flash will work too but I personally like ghost more.

I choose to go this way with items because of lack of survival with pantheon and easily getting shut down if you got sword of the occult so this is why I skip it.

Item build:
You may wonder why Dorans blade?
Because of the early 100 hp, early 8 damage and 3% lifesteal which really doesnt have much effect, But instead of long sword like many builds want you to start with it only gives 2 more damage but no hp no lifesteal, which is why dorans blade is more viable as a first item.

Next item is preferably BF sword, but if you can not afford BF sword but still need to recall so desperately get Brutalizer or boots of your choice, I like swiftness & Mercurys but I'd rather take swiftness against little cc but mercurys against alot of cc.
As DEWO states in his own builds he says it's best to get BF swords before getting full BF item. Because stacking BF swords is the best AD per money you can get.

Depends on how fast you got BF Sword/Brutalizer/Boots you will try to get BF sword before everything but after your first BF sword I recommend boots then another BF sword leading to finally brutalizer.

Now you should be building on to your Bloodthirster for starting to stack that 100 damage, When done with Bloodthirster get Frozen mallet/Banshees veil/Warmogs, whichever fits you the best and the opposing team, sometimes I skip black cleaver for banshees veil which gives more mana and magic resist since they shut you down pretty well.

Now after frozen mallet the game should be over and you should have been dealing alot of damage to the opposing team, if game is not over get Atmas impaler for more damage, obviously if theres someone really fed on the other team shutting you down you should try to get some defense against that person. Quicksilver sash could be some kind of alternative item.

After atmas impaler get black cleaver if you got banshees veil/warmogs instead you could go for youmuus and consumable elixirs. Game should be over now.

A tip for laning: GRAB MANA BUFF ALOT.
Laning: Play very agressive but not too agressive so you run out of mana, make sure you last hit alot under the first 1-5 levels. At around level 6 you should have last hit enough or scored a kill or two to be able to recall and ulti back to lane.
At around lvl 6 you will be a killing machine if you managed to get your BF sword so as long as someone is alone you will problably have the advantage, don't be stupid and go for 2 people all alone unless they are very low on hp, have common sense :)

Team fights break out around lvl 10-11 which you will be having good stats if played well, and blablabla :P

I have gotten great scores with this build myself.
This guide is problably very outdated now and i'm not very positive if it's even working with the current changes of pantheon, Since his HSS was increased i'm problably going to just leave this as it is and going to make a new build.