Well first of all sorry for the bad englis and i dont want to write a long guide. ( if u guys like it i'll describe everything)
Pantheon is a strong AD based assasin, he got nerfed several times.
The reason why am i using this build is very simple : you can get nice stat with a pure ad build, yeah, but later (mid and lategame) you will be focused, and that means you can't do any dmg and die first.
Joggernaut + Mercury's threads will save you from this problem.
Also you are not a glass cannon :)

Pros:
-high health ( 4500+)
-hihg defense
-nice damage (~310 ad)
-awesome stun
-awesome diving (by your passive)
-if you got slow computer, you are able to survive a larger lagg

Cons:
-nerfed spearshot
-nerf range ultymate( great for saving turrets or just to travel)
-could be hard to play first time
-most of players who cannot use this champ will blame you for buying tanky items

Core items: Mercury's Threads , Phage , Infinity Edge

Recommend items from me : Frozen mallet , Athma's impaler, Force of nature, Warmog's armor
Frozen mallet: slows enemy + awesome health bonus
Athma's impaler: you are low on ad so it grants u ad from hp
Force of Nature: grants movement speed + increases your healthregen from your max health( when u buy it u must have about 3000 health so its a big help)
Warmog's armor: finally more health ->> more ad and more health regen, now you are nearly immortal

Items what you should never pick:
Phantom Dancer: you are a caster melee not an auto attacker
Vampiric Scepter: got healthregen, not autoattacking that much, its pointless :)


Items that you could use, but i don't recommend:
Trinity force: however its a nice combination of items, but we still dont need attackspeed
you can swap Frozen mallet to this item at the very lategame (cus with 310 ad sheen's passive starts to be interesting and you lose only 400 health) but i still Prefer frozen