Ok lets start this off with this quick note

This jungle guide is meant for 'Normals' not ranked.

Janna is a very fast clearer and amazing ganker.

This guide will help you have alot more fun in the jungle.

Pros:
Fast clear speed
Able to start boots 3 due to shield
Great ganks
Shield is almost always up

Cons:
Blue buff hungry "Best used with mids who dont need it"
Miss your Q and your gank lost half its potential
Needs a decent leash startgame

9 - Magic pen marks
9 - Armor seals
9 - Flat AP glyphs
3 - Flat AP Quints

These runes are built around AP Janna since you will be farming a fair bit

The armor seals I choose to use since nothing else really helps her jungle

I choose 0/21/0 Because she builds very glass cannon mid game

Helps her take a few hits in a team fight

Helps her sit in a jungle camp and not take any damage when shield is down

Smite - goes without saying

Flash - Because really what else would anyone use these days Flash is just to good

Potentials:

Ignite - If you dont like flash ignite is your second choice

Ghost - Escape like speedy gonzales

Possible jungle starts include

Boots - 3 Health potions

Cloth - 5 health potions

Amp totem - 1 health potion (Only if you completely trust your shield) and get a great leash

Early/Mid game

Will of the ancients is great for jungling without blue Q yourself to full health

Deathcap is just the best ap item in the game

Void staff - This item is mainly picked up against high MR Champions

Lategame:

These builds vairy lategame it depends mainly on what you are vsing

Possible lategame:

Lichbane
Banshees
Amyssal sceptre
Rylais crystal sceptre (The tankyness helps but I never use this item)
Warmogs (This is an 'Ok' Choice if you want to take a few more hits)
Zonyas hourglass (Cmon, Who doesnt love invincibility)

First path route consists of:

Wolves (With help)
Blue buff (With help)
Wraiths
Wolves (Again)
Red buff
Gank - Or golems
Wraiths
gank

The rest now depends on which lane is pushing and which ones arent

Example:
Enemy top lane has pushed to tower
Gank top - Kill golems/wraiths

Congratulations on stumbling apon one of the most fun junglers I have ever played

You know have an idea on Janna jungle but as this is a guide things vairy alot ingame
So be carefull you might get counter jungled
invaded on blue

Just keep in mind that no matter what they do to you.

YOU ARE JUNGLE JANNA!