Now with the buff of Frozen Domain (W) to 20% increased heals from all source **at all levels **its a no brainer to pick him as a jungler instead of a laner. I've been playing him for 4 years now (its sad) and I've never been able to come out a 2x full jungle sweep with all of my health in tact. He can live and out level the enemy jungler. I usually build:
to start him off.
He's mana hungry, if you ever do play him. I start off smiting gromp, go to blue, use a pot WHILE ON FROZEN DOMAIN to increase gain around 4 additional health points per second. I'll be full health by then, go to wolves, wraiths (pop a pot), then red. I'm usually never afraid of it getting stolen, but have an ally ward it if you are. Get golems if you want the extra gold, but you'll usually never need it.
Optional side quest: Gank bot/top after blue buff since no one usually wards so early.
Go back to buy:
And gank until blue buff comes up. If you're confident enough to invade, now is the time for deep enemy jungle warding and pink dragon warding.
This here is a must on your next buy:

unless you need armor asap, i.e. heavy
in addition to the adc and top laner get:
--->
Even though I'm a jungler, I'm trundle, I have nearly nor realiable gap closers, but I do have a slows and a non-reliable knockup. I buy:
and work my way to a
before OR after i get my tier 2 boots. Because you'll have more than enough movement speed (MOVEMENT SPEED QUINTS IS A MUST) @ around 475 with frozen domain.
So a mid-late game build will be around

people say
is a must, but
deals more damage. Period. If you're ahead or on track get
. Otherwise, go for defensive items such as
---->
. Health items are always better on trundle then other defenses since he'll steal armor and mr.
Depending on the team comp and how far behind / ahead I am, I'll then get about my
if I'm not the only melee champion. If I'm the only melee champion or only tanky melee champion, I forget about all other damage and focus on keeping my team alive.

AP Heavy: 