This guide its based on own experience.

I focus the build in critical strike and attack damage, also has good health, armor and magic resist to resist against enemies, ignoring cooldown reduction.

Mark of Desolation:
Armor penetration its useful to fight against tanks, in total our champion has 33 points of it, against mages its more useful because our attacks hits pure damage.

Seal of Defense:
Armor its useful to resist melee enemies very good and resisit in battles, also the emblem of Pantheon its nice damage and good defense.

Glyph of Shielding:
Until now we have looked up for melee enemies but mages are strong enought too, so to resisit a battle and deal considerable damage we need provide defense against mages.

Obiusly this its an offensive pantheon so we use 21 points in offensive tree ignoring ability power, cooldown reduction and havoc for this reasons: we focus our attack in melee damage, thats our "ability power" (all our skills are based on base damage), cooldown reduction its useful for any champion but in pantheon its not a big difference with or without it, and havoc the same, 1.5% damage dealt its not a big difference because we hit critical every time, for example hitting 700 or 709.5 (+1.5%) doesnt make a change.
In defensive tree we use 6 points increasing armor and magic ressistance because runes without masteries are useless.
Then we use 3 points in expanded mind at utility tree because helps a lot our manamune passive ability increasing damage.

We start with meki pendant for a short reson, we use spear in early game and it has a short cooldown so we spend a lot of mana in this ranged spell.
Then we choose vampiric specter to regenerate hp attacking minions.
Then we buy berserker's greaves to get a faster farming and avoid enemies gank or escape from a battle.
Then finish manamune recipe because can support our 3 first skills and add damage.