Hy thats my first guide on moba, also i´m sorry for my english, but you should undestand all i want to say^^. i hope you enjoy the way i like to play Fioara, its nearly the same way i play talon because she seems more like an assassin to me. I play her only solo top because there are much better champs to jugnle with with some ccs like xin or noc.

Pros
+ 2 Gap Closer in short time
+ AS burst
+ could block one auto hit, good against empowered hits like from nasus or jax (dont know if it could block gp´s q)
+ invulnerable while ulti, deals nice dmg

Cons
- easy to counter
- squishy
- easy cc ed to death
- no cc, not even a slow

I like to play her full dmg exepted of guardian angel.
Here is the reason why i buy these items.

This item helps you to stay in your lane and gives you lifesteal you need to regg while your ulti.
Ad, As, Crit, Movement Speed, health, slow, adn 150% more dmg on hit effect (it also should work on your ulti). A nice item you really need to chase your enemie and dmg him more effectly
you need them for lower cd on your skills so trinity force would work more efficiently.
More Ad, more and higher crits, what do you want more?
More Ad and more lifesteal = more dmg autohits and more dmg and lifesteal on ulti
With that item you have a way more survivability and you could drop 2 times low (first time ulti use 2. time passive effect guardian angel), you also could buy warmogs or banshees, but i figured out that guardian is the best :)
Last Wisper Ad dmg and armor pen, more situational, you also could buy black cleaver or madreds.