Hey guys,
I've played Sivir many times on my previous accounts (DareTheDrake and Dracco Dare). This guide should help you with getting the right items if you need more mana early.

Long story short:

Sivir is one of the lower-priced champions that can help team to gain the winning edge in matches. Since it's mainly played as ADC, her Ricochet (W) ability and it has a wide use, and can poke enemy team's champions and take down minions at the same time at the lane. (If you don't know the ability, it's basically the blade that hits many and ricochets to another).
The Boomerang (Q) is mainly used to poke or damage and last hit enemy champions. It does 25 / 45 / 65 / 85 / 105 (+50% of ability power) (+0.7 / 0.8 / 0.9 / 1.0 / 1.1 of total attack damage and the damage can be boosted by buying the listed items above.

Spell Shield ability (E) is interesting with it's Defense-to-gain-mana effect. If Spell shield is used when enemy champion casts a spell at Sivir, Sivir regains 80 / 95 / 110 / 125 / 140 mana. If player (Sivir) is not so good at blocking spells at right time then she will need the mana regen items. Again it depends on the player's (Sivir's) playstyle and experience.

The Ultimate, On The Hunt (R or T) ability has the best effect when nearby friendly champions are around. When casted, it grants all nearby allies an initial 40 / 50 / 60% Movement Speed bonus that reduces to 20% after 2 / 3 / 4 seconds. So it's a great help if Sivir and her teammates are chasing an enemy champion or if they need to flee from a fight.

There are other sources, i.e. Vapora's Guide To Sivir that tell you a lot about this Champion, feel free to visit other builds.


The Mana regen

It happened to me a lot of times, that I was running low on mana few minutes into the game, probably because i used Ricochet and Boomerang ablity a lot. Buying Athene's Unholy grail or at least Chalice of Harmony helped with this problem.
There's one alternative item: Frostfang, it boosts mana regen by 50% and lowers the Cooldown time by 10%, so if you dont want just mana, this is probably the item of your choice.

Runes are not included in this article. Its not necessary to boost mana regen with Athene's Unholy grail item. Armor and Attack Damage boosters are probably the best choices for Sivir.

Good luck with Sivir!
Dracco