Start:
I always start with boots and 3 Heal Potions.

Midgame:
I buy the Items there on the picture

Lategame:
I switch between "The Black Cleaver", "Infinity Edge", "Last Whisper" and "Entropy".
I use "Last Whisper" when I play vs players with good Armor and "Entropy", when i need to be more tanky and when i need more attack damage, i switch between "Entropy" and "The Black Cleaver"

It's very useful to play with a supporter like: Soraka or Taric. You need Soraka's manaheal, because you haven't good many mana.

It's very easy to farm with her.

First:
Do your "q" and hit them, then you can do you "w", when they aren't dead then you can lasthit them very easy.

I play Sivir with attackdamage and mana, because i lovely play with her skills and not with her autoattacks. For this i buy very fast "Tear of Goddess" and I always use manareg masteries.

I hope you enyoned my Guide, it was my first one

For all grammatik fails, I can say I am german, but I hope, I helped you :D