Well, on this guide im going to show you a total ad ferrari assasin build for Hecarim, just try It and comment!

For runes, the best suggestion is
Armor Seals
Attack Damage marks
Magic resist Glyphs
Movement speed Quintessences

You can also change the glyphs for armor glyphs as well
and change attack damage marks for armor pen as well Greater Mark of desolation but i think that with armor pen u got goes pretty good, and without attack damage runes the jungle might be harder

This masteries gives you the best movement speed for hecarim, as you know, hecarim gains attack damage from a percent of his speed, so its a viable choice.

This items, as the title says, its just for full ad hecarim, if youre trying to be a sustain hecarim or tanky hecarim, i will make another tanky guide for him.

your is your main source of damage, so you have to maximize it first, but dont forget that your is your sustaint skill, so you have to consider to take at lvl 4 for more health gaining. your is an utility skil, so maximize it last

I see
and obviously for jungler hecarim
but you can also try instead of