Hi welcome to my first build, Fiora just became avalaible and I didn't see some guides that just fit she as well as I want to.
First of all I just want to say that I'm french so my english may not be perfect, but I do my best ;).
Basicaly this guide is focus on damage and attack speed, Fiora is a real beast and can deal very strong and fast damages.

Hope you will enjoy.

I'm not a real runes expert but speed + attack damage is the main purpose for this choice.
May some more armor and magic resist will be prefered if you play against strong opponents.
Also I do not pick armor penetration but if you think it could be used, replace some Mark.

As Fiora is a new Champion, I could not test every runes build.

pros
+ Very fast (+70% attack speed at level 2 !)
+ Hight damage early and late
+ Nice farm
+ Excellente combo
+ Good harasser
+ Love her ulti <3

cons
- Very squishy
- Items dependente
- Can be harras
_ No escape ability
_ Mana ...

Ok about item, it was hard to fix one build because it really depends of the team in front of you. I start with boots because you are easily focusable, it will give you survivability.
Then some attack speed is the key, after your bow, you can start gank (you are level 4~5) and get gold from kills. Your speed combine with your abilitie give no chance to ennemies.
Keep in mind to only attack one guys at the same time, you are still squishy.

Then the boots are finish, you can farm pretty well, if you can, a blue will be necessary and can be done without losing too much.
Finish Wit's end, you now deal very strong damage. Feel free to leave your lane from now and gank every where.

Next some lifesteal will increase your survivability (multiple gank will hurt you).
And the damage from Bloodthirster will increase your capability. Be sure to fullfill Bloodthirster passive.

Next item are very variable, if ennemies already fear you, take some more damages and critical strike. Else, if strong ad take Thornmail (basically for the armor, bonus the badass passive :D), strong ap Banshee is nice or a Quisilver Sash. Also armor penetration can be necessary.
More speed isn't necessary because of your ability, more lifesteal could be great, adapt your choices.

Fiora 'e' is one of her best early abilitie. Maximize this ability with 'w' and you will give really strong damages.

Her 'q' can only focus ennemies, nice to move forward or escape if you have creeps behind. But not very usefull after a gank when you are chase.

Her combo are really impressive, use 'q', and at the same time 'w'+'e', this will give a tons of damages, after that, escape of finish with another 'q' and 'w' or 'e' when availables.

Her ulti is a damage dealer + a protecter, you aren't focusable when activated. Use it very often, but be warn that you will hit the first guy you focus at the last hit. If he run away you will appear behind the ennemies lane... And die.

This is why flash is usefull, you will escape easily from ennemies when you are in danger.

Finally keep in mind that your combo consume a lot of mana. A blue give you mana + colddown, it's very appreciable. You can also pick up ennemies jungles if they aren't very vigilant.

Just a short paragraph about Farming, as you are items dependant, a good farm is necessary. Early you will have difficulty to farm, specially if ennemies harras you strong.

After your first kill (or second) you will have no problem, your speed give you very fast farm and ennemies will fear your combo. You can also empty ennemy jungle.

But the main gold ressource is your kills, try to kill as soon as possible, hunt the alone guy, search the jungler. Move every where. Farm creeps when possible, return on jungle.
If you have ever play an assassin, you will enjoy this.
And from mid or late game, you will have the best farm easily.

Finally you can detroy a tower from level 12 very fast. If your team run out of gold, do it, it will pissoff ennemy team and bring gold to your's, just prepare your escape with a flash or you will get caught and it's not resonnable.

We arrive at the end of this guide.
I know some people (including me) only read introduction and summary so I will try to resume all.

In this guide we have try to maximize speed and damage or Fiora, you will easily get many kills.
It really enjoyable to see ennemies rage saying "Riot new champ is op" (true story).

Personnaly I have actually never lost a match with Fiora, these items give strong early damage, and ennemies surrend very soon.

This is my first guide, I hope you have enjoy it, I will try to expand/add some sections.
If you see some mispellings, please say it to me, I'm sure a make a lot ^^