Heya fellow league friend. I mean no offense to you, but there may be parts of your guide you may need to consider. Lets get to it! :p

You dont have any form of magic resist, so u will get 2 shotted late game, you have no form of tenacity (mercury treads), so late game stuns = death, you put too much focus on armor pen quints, when if you do your math correctly, red armor penetration marks will be enough to get panth to deal "true" damage, cuz the max armor someone can normally stack is 18, put ur quints into attack damage, you need magic resist for runes, as magic damage will deal true damage to you, buying doran's blades slows down your overall build, it'd be better to build immediately into a vampire scepter and get better health benefits, you dont stress the needs of wards, you give panth no form of mana, so after two rounds of attacks, he is mana starved...and that is just the build and runes. If this is the way you play panth, fine by me, but I would not suggest this guide to other players as it may not offer a "balanced" playstyle for pantheon.

Hello and good morning :).Well.The build is not bad for normals.But i would probably take Mercury treads instead of Swiftness.
Consider adding a list with some situational items as well.
SOTO really sucks overall.It will either make you godlike,or drag you down in a ****ty game.
This is a risk not worth taking,especially against people who know how to play.
Although Atma's is a nice item especially for its cost but it wont deliver the damage other items can do if you have 2,7 k health.You probably need more.

For skill lvlup I suggest taking Aegis on lvl 2,but whatever works for you.
Masteries look fine,although I prefer using 8 on defence.I am working on several pages right now and there are many things you can use and experiment with.
So this is my feedback :)
Gl & Hf!.

great build but 1 problem
clarity is NOT worth it.
by the time you run out of mana your level 6 you go back and buy sustenance
if the enemy got exhaust or ignite youll lose your lane HARD
and boots of swiftness >.<
your early damage is just **** your not playing early game pantheon, your not getting early kills because you have no ignite, your boots dont help
your late game is still good but you really need to take another look at early game cuss this just aint working

its personal preference for summoner skills i like taking flash and ignite to burst then gtfo :D +1

good guide :) +1
However I do believe that pantheon should be played with exhaust/ignite or even both. Pantheon should not be mana hungry if you only farm and harass once an a while. If you need clarity, you probably are spamming skills, and you arent hitting 100% or your spears. Pantheon is a killed or be killed character, as you state with no natural escape. Exhaust or ignite are needed.