This is my Fiora build, I created it kind of in a rush but I'll explain step by step what to do and how to retaliate in fights and team fights. This build so far works perfectly in 3's but unsure in 5's.

I take a lot of thought in being a little tanky in the first gank on 3's. So I take armor for the annoying ad's on the enemy team and take magic resistance for those ap's that decide to poke the bush with skills.

I take all ad masteries including the ignite and flash mastery. Then max out the magic resistance and armor masteries in the defense section.

A lot of people get W first for their first skill but I don't see the point because sure you get damage output with it, but if they flash away and you've already wasted your flash how are you going to catch them? With this build using your Q first is a must! It gives you 4 hits to kill someone. Use your Q then auto-attack, then use your Q one more time and auto-attack again.....if he's not dead use ignite to completely demolish them. However, when leveling everything up, max your W first for defense and for the extra damage caused to your enemy. Then max your E second for the movement speed and attack speed. Max your ult as normal.

I take Flash and Ignite because flash helps with jumping over walls and used for the offense and defense of team fights. Ignite enemies either when they get away or when you use your ult. This will cause the enemy to get weaker from both your ultimate and from the true damage of ignite. However, you can substitute one of these for exhaust for slowing the enemy and making their damage low.

Now during 3's....You'll need top for this build to take the full effect. Starting with doran's blade will give you damage + health + life steal. Next you need to get boots of speed and some health pots (get as many as needed or don't get any at all). Then grab a cloth armor or vampiric scepter. Complete your wriggle's before you complete your boots so that you can have your sight warding ready for team ganks. Depending on the enemy team grab either mercury treads or ninja tabi for a little resistance to enemy attacks. After, start working on your black cleaver for total damage from your ultimate. After that, if the enemy team is building health, build madred's blood razor, if not build an infinity edge. After this item, grab anything typically tanky like a guardian angel or you can choose to go blood thirster so you can have better life steal. After those items improvise because none of my game lasted longer than the items I just mentioned.

Pros:

+ Very big burst damage
+ Can ace the team
+ Can get called a hacker

Cons:

- A team with CC will destroy her
- If focused then your screwed (unless your team knows who to focus)

This is a build that I created myself. Thus far, I haven't caught another Fiora defeating me when I build these items, namely because of my black cleaver and their wriggle's. But, hope you enjoy this build and get over 10 kills with them.