Hey, this is my first guide on MobaFire yet and I've been wanting to give this community something back for so long.
Before you vote, please take your time reading through this and please be taking my decisions into account, as I will state why and how i decide most stuff.

Please keep in mind that this is my first build and that I'm going to be improving it as I improve my gameplay with Hecarim, as well as the formatting ;)

I'm also open for any suggestions that you may have in mind or already tested out! Please leave a comment :)

Without further stuff to read through, let's get started, shall we?

So, yeah, an introduction. Is this meant for the build or me? Just kiddin' here.
This is a DPS Jungle build, obviously by the selection of items I made.
It also contains a little bit of sustain with a healthy approximate ~100 - 120 armor and MR.

Pro:

GREAT ganking potential, even early-game
Awesome specs
AWESOME Roaming
High DPS
Awesome skins! ;)

Con:

Not doing well if jungling slow / underfarmed
Very Item-dependant
Isn't female (lol)

These are my personal Pros / Cons. If I'm missing any, point them out!

The choices here are pretty standard. These are my general AD runes, which I feel most comfortable playing with, except for the quints.
4,5% additional Movement speed equals a default MS of 334.4 (334).
With buying boots first you are getting around ~375-ish MS.

For the lack of Sustain we have in the itembuild, we will take masteries that will benefit his survivability abit more, while aswell trying to squeeze out as much movement speed as possible.
Not much to say here.
0 / 21 / 9

The interesting part.

"Why do you buy these items?"
"Why in that order?"
"Where is the DPS you were talking about earlier?"

These are the questions you might ask yourself if you haven't played Hecarim before, or if ou just don't think this'll work.

I buy these items because they give me exactly what I need, and more importantly, what I want.
Movement speed, which scales his AD up, attack speed, which is just wonderful, critchance for the little extra damage you might want to pop on that low-health enemy, and some sustain with CDR.

The order is pretty basic (with exception of the Boots first, then Madred's).
I don't buy a Wriggle's because I simply don't need it. You could however buy it and replace it with the Bloodrazor endgame, it's just not my style of playing a jungler (I never get a Wriggle's, don't judge me ;) ) and Hecarim is pretty sustainable with a few pots and his W.
The attack speed also helps with the sustainability, especially when facing enemies, but we will come to that later.
Note: if you feel that you need sustainability asap, buy Force of Nature / Frozen Heart (depending on the situation again) BEFORE Phantom dancer or even before the second zeal! I myself haven't had a situation like that yet but you never know, every game is different!

Ofcourse the sustainability items are situational. Are you facing enemies that are mostly AD, go frozen Heart first.
What? Not so many AD? None at all? Go for Force of Nature after you finished the Phantom Dancer. If there really are no AD champs at all, get a Banshee's instead of the Frozen Heart, it's just not included in my build because I usually am not facing any pure AP teams in my games and I don't want to confuse people.

Madred's Bloodrazor for the bonus % HP damage, the armor and AD/AS.

The DPS is as explained above hidden in the movement- and attackspeeds. The faster he runs, the higher his AD is. Spamming your Q with a roughly only 1.8-ish second cooldown (counting the stacks already in) the Trinity Force really is worth the price.

Skill sequence. It is essential. Always initiate a fight with your charge (which procs awesomely with your Trinity / Sheen). RIGHT before you arrive to hit the enemy, pop your W.
It will heal you if the enemy was "ready" for your assault and already attacked you from afar (Try to time your charge correctly. You gain more momentum as time goes by, for a maximum timeframe of 4 seconds. The more time goes by before you hit the target, the more damage you deal).
If you landed a successful hit at your enemy, he or she already has lost alot of health. Instantly use your Q again to deal some additional damage and throw an auto-attack at them, since your Trinity / Sheen already proc'd again. Repeat Q#ing to charge Trinity / Sheen and mash with auto attacks.

Try to spare your ultimate, do not waste it. Use it to stop / kill low-health fleeing enemies or pop it when theres more people coming for you / your teammates to deal some significant AoE damage (Trinity / Sheen proc'd again, use it! :P )

Jungling is basically the same as with other junglers, it however depends how you jungle. I typically start at blue, go wolves (pop a pot after blue, or during blue if no one pulls), then wraiths, golems, ask top to pull red if he / she / they are doing well, go wolves again, go wraiths, go golems, return to buy Berserker's and Madred's.
Of course, if necessary, go mid if your Mid-laner needs help in between second wolves and second wraith camp (don't kill creeps if they need the farm, ask if you are not premade!), or just hold lane farming creeps 'til he / she returns.

Gank as often as possible as soon as you hit level 3! Charge is just a very nice skin, too nice to ignore. "Backdoor" from the river if they pushed too far, charging them, pushing them even more in turret-range to get these easy early-game kills.
I'm open for other suggestions! Comment below ;)

Yeah, I know, my formatting. I will work on it as I improve the guide and get into more detail on all the stuff (also creating more chapters, I know there are some that are missing, like alternate items and stuff).

Bare with my English please, I'm no native speaker! If you come across any mistakes, point them out and I will correct them ;).

As I said before, please comment all your suggestion, alternative builds, criticism, compliments, whatever you feel the necessity for.