Welcome to my Jungle Rengar guide.
This one build is based on what i find suitable for my playstyle with focus on damage with sustainability. This builds rengar as a mid-tier jungler that can come out ontop from any situation.

DO NOT only use the item purchases and runes. Take your time and read this guide as it take a certain playstyle for granted. If it fits, try it out and let me know what you think of it

The items part of this build is subject to ingame changes and you need to be aware of that.
Sticking as far as Phage is fine, but then you will need to decide.

Being the teamplayer
As the jungling ends with you taking down the first couple of towers, your main focus will be to assist in teamfights. This means you have to be alive and kicking most of it. This build is not for getting Rengar any 99/0/99 stats but to be a teamplayer in all ways.

Take notice of the damage output from the other team. Getting Negatron Cloak, Thornmail or Guardian Angel when needed.

As rengar is the perfect predator for ganking, you need to do this from level 1.
Make sure you get red buff instanstly with the help of your friends
There is time to get wraiths before red spawn and that will get your to level 2 before anyone else. Get Bola Strike as your second skill and make sure to lock that top gank down.

Getting Firstblood
The absolute best approach is to stand in bush below the toplane and wait. Take notice of how long you can leap with Unseen Predator and lock that champion down with your Bola Strike. Let that bola be your 5th and last Ferocity loadup and use it all on either locking the enemy in place with another Bola Strike or do some massive damage with Savagery

When the laning phase ends you need to support your team. Making sure to get the buffs for your AP and AD carries and stay by them!

Let your predator feelings simmer down and become the teamplayer that is now needed. If you get Randuin's Omen, make sure to set it down in every teamfight you get into. The debuff is crucial for the teams success.

Another reason to become a proper teamhugger is that you do no have enough sustain or damage output to take down 2-3 champions if they find you in a compromising position. Leave that to your fedd carries

I focus on a mix of AD and Armor for rengars Jungle. We want as much of both as possible.
Other viable options include Magic Resist or Armor Penetration