Please mouse over the "+notes" in the item section above.

You don't need crit on Sivir because her base damage is so high. She functions more like blue Ezreal than a traditional ADcarry.

With this build you are amassing cooldown reduction and armor penetration. You don't need attack speed because of all the CDR you have accrued. You constantly use your W(ricochet) as an attack speed reset with 25% from items+4% masteries=29%. Furor boots work well with her passive and ultimate but of course homegaurds are a good buy.

You don't build lifesteal early. In lane you should be able to farm easily with HP pots, Q(Boomerang) and E(Spell Shield).

For summoners I like Ghost and Barrier.
Ghost is much better for extended team fights and it also works much better with her ult and passive. The only time I would use Flash is if I'm vs Jarvan.
Barrier I like just because it's good.

Cooldowns with 29%
Q - 6.4 Boomerang
W - 2.1 Ricochet
E - 7.1 Speel Shield
R - 56.8 On The Hunt

PROS
about 1500 gold cheaper than a typical AD build
very high damage output
very high AOE damage
great poke
low cooldowns
difficult to focus
great wave clear
fast pusher
high kite potential
high chase potential
high dueling potential
removes the manacost burden that normal Sivir builds suffer from.

CONS
None.