This is a work in Progress.

Pantheon is pretty beast in 3's. This build is more of a Bruiser build, if you die a few times and want more survivability.

I get a Doran's Blade to start for that extra damage.
Boots of Speed for extra movement.
Madred's Razors and Wriggle's Lantern to lane better more sustain and jungle.
The Brutalizer mostly for the cooldown reduction but everything on it is nice on pantheon.
Phage Makes it a little easier to stick to your targets and extra health is nice.
Sheen It's passive is nice plus, the extra mana is good for Pantheon.
Trinity Force just an all around good item.
Upgrade The Brutalizer into a Youmuu's Ghostblade Then I move it to slot 1 on your Items it's on smart cast and I always put my Active items on slot 1.
Replace the Doran's Blade whenever you need room and buy.
Infinity Edge Also a great item.
Replace the Wriggle's Lantern with The Bloodthirster.
Then buy some Elixirs.
It's also nice when you have 250g but not enough gold to buy your next item just buy Elixir of Fortitude.

Also when you recall buy a Sight Ward or in my opinion a Vision Ward.

Put the Vision Ward at Dragon or Red Buff then you can drop your Wriggle's Lantern somewhere else where you might get ganked or in the top bushes in jungle.