Hi there, Test User here. Jungle Fi is one of my favourite champs/styles to play because she is a hard hitter, and if played right can get a surprising amount of ganks in early game while scaling amazingly into late.

I just use the runes I do to cover the spectrum for an AD carry really. Attack speed and damage runes are good general purpose ADC stuff, and the armour pen really helps because I don't use any armour pen items in my build. The quints are set up for more sustain in the jungle and bit of defense because this build also forgoes that somewhat in exchange for the sustain provided by lifesteal.

I know lots of people like to do the 21 and 9 set up for masteries so they can get the last mastery in the tree and move on, but I use my regular ADC masteries, plus the extra 2 in Butcher for the extra jungle spice. Since I don't focus on high health items with Fiora, the health masteries lose some of their use, so I use the health regen and minion defense for sustain in the jungle.

So I've seen a lot of builds that craft Fi into a sort of off-tank bruiser, but I don't think that's the best use for her, especially in jungle. If you want an AD off-tank top or jungler, Olaf is just better built for that all around. I think Fiora's specialty is lots of damage, quick, and I think that's what should be emphasized, especially early game for ganking. I've read that Fi is not optimal for jungling because she doesn't have CC, but I think there are other ways to play her strengths as a great jungler, by using good positioning and tactics to gank, rather than leaning on CC. So how this relates to items: I like to stack the damage right away, then add some attack speed and tad bit of health on later, as they become needed past the jungle phase.

Fiora's best ability is her Burst of Speed. It's great for clearing jungle, doing lots of damage while ganking (a large part of what makes her viable as a jungler), and it's great for chasing or running. Her Riposte adds a great amount of attack damage, helping make her such a hard hitting champion. The extra 15 damage from just the first rank is like giving her a free early game AD item and a half (longsword) and provides her with a huge edge early game. I take lunge third, because it is best for it's effect of lunging, and the slight bit of damage that raising the still adds is kind of a side effect. I like to get lunge at third level though for it's effect. Once you clear the first jungle wave, you have each of your abilities and it's prime time to gank.

For spells, I feel like Smite is a pretty obvious choice when jungling, especially since Fi doesn't have too much sustain early on. Flash is my favourite spell for her and I think it's definitely her best fit, because her play style is all about getting in and getting out quick.