to my solo top guide for Diana,
In this guide I'll show two ways how you can build her successfully.
The one way is a "Burst"-Build which allows you to deal tons of damage and the other more tanky one allows you much more sustain but a loss in the matter of damage.

Reason for the first build is self explained, because everyone wants to deal alot of damage, but why should we have a look at the second build too?? It's simple Diana is a close combat champion even if you are more like a caster, because of you ultimate which is a great gap closer you will usually stay close infront of a enemy so if you cannot react fast you will die except you have some sustain!! Another reason is that we have allready a mid champ in our team which usually is an AP caster.

+ Burst Damage
+ new Champion - no or at least just few tactics to counter her
+ great escape ability
+ new kind of CC (AoE pull) :>
+ low ultimate CD :P

- squishy without tank items
- needs mana (Assassin champions like Akali don't need)
- level 1-4 weaker than most of the solo top champions
- and alot more things :P