Hi, I'm Jamie and welcome to my jungle Malphite build.
In this guide, I will describe how I personally play Malphite with possible exceptions that may differ with your own personal play style.

This is my first guide so chances are this will have a bit of editing to it until it looks good. Please don't downvote just because it's poorly laid out or because you disagree with it.

Pros:

• Granite Shield allows him to take free harrass.
• Good CC/self buff with Seismic Shard
• Counters enemy ADC with high armour and Ground Slam's AS debuff
• Great tower diver
• AoE knock up
• Fast jungler

Cons:

• Difficult to escape when ganked/retreating
• Quite an expensive build
• Scales off AP/AD and armour so can be confusing to build for or to scale runes.

First we will look at how I build him and why.

I jungle 95% of my games with him and have thus begun to rely on Ground Slam as my main damage dealing ability while still playing him offtank. This works in favour as Ground Slam scales off 30% of your total armour so it's logical to build like that.

During fights vs anyone that isn't a squishy or where you're trying for a kill, Malphite tends to run low on mana after a combo or two so to counter this, some mana regen/5 was implemented.

Unless you're vsing a heavy AP team, you're items won't really have anything in the way of magic resistance so to counter that we have the MR/level so we still have an adequate amount of resistance.

Lastly I have magic penetration runes. Now this one is completely optional depending on your play style where if you prefer to use your abilities as CC over DPS (I.E in the case of support), you can then change them to armour penetration. Either way, it's more damage but I chose the MP because all three of his offensive spells are magic damage.

One thing I like about this build is that you can clear jungle with the use of one HP pot so that gives you over 100g spare.

I start off with the said 1 HP pot and a Cloth Armor for extra defence.
After you clear jungle for the first time, come back and turn the Cloth Armor into Ninja Tabi then start getting items to build into Guardian Angel. I rush this for the extra armour to scale your Ground Slam to clear jungle faster and to help with ganks or diving without dying due to the passive.. Depending on the enemy team, you should get a Cloth Armor first if you have no issues or a Null-Magic Mantle if their AP is harassing too much.

After that, get Randuin's Omen starting with Heart of Gold for the gold/5 then grabbing Warden's Mail before finishing. Make sure you put the item in an easily accessible item slot so you can use the active effect during ganks/initiations/team fights. It's perfect for easy kills.

After that, Thornmail is good for the extra armour and is a great counter against ADC but is very situational. If you're not the focus of attention, you may be better off getting Sunfire Aegis now. That will give you armour still but will also give you HP to increase your passive Granite Shield. The AoE is good since most of the time you want to be in the thick of it a it's always good to pass off free damage to anyone who wants to hang around.
Pick up Glacial Shroud and finish off with Frozen Heart for the CDR aura and AS debuff.

Lastly, (If you get this far) pick up a Frozen Mallet for the passive slow and extra HP to buff your Glacial Shroud.
If you're facing off vs an AP heavy team and are having some difficulties, try replacing Thornmail with a Force of Nature. This is effective while farming jungle.

Switching from Ninja Tabi to mercury tread is also a good idea.

If you're playing support, try picking up Frozen Heart a little earlier to help your carry with their CDR.

If you're having your own mana issues, pick up a Faerie Charm and build it into a Mana Manipulator.

If you do choose to build MR over armour, building HP items over armour items might be better so rather than Sunfire Aegis, you could try Aegis of the Legion.

Start with Ground Slam to clear the Blue out faster. If done properly, you should level up to 2 after that to get your Brutal Strikes for the passive splash damage and armour increase for your Ground Slam.
Get your Seismic Shard at 4 then use it to gank. Max Ground Slam getting your ult when you can. Max Brutal Strikes next for max damage/tanking but if you're having issues with escaping enemies then maybe max your Q but it's probably not enough to capture those kills.

I'll do a jungle tutorial video for Malphite at some stage and embed it here.

~Watch this space~

In short, jungle -> build tanky (which gives you damage so you're not losing out) -> gank hard, -> feed your carries -> win.