With how easy it is to kill a ton of minions very quickly with Sivir's Ricochet ability I would think warmogs would be an item that people would like to buy. It would give Sivir a very nice HP boost in order to stay alive in team fights so you can support your team longer. I haven't tried it yet since I am not able to play at the moment but I just wanted to see if anyone else tried this.

Oh and the reason why I am asking is because I looked at the guides for Sivir and didn't see warmogs mentioned.

I use Warmogs every time with Sivir. I usually roll something like this:

Cost - Item
390 - Meki Pendant [Mana Regen]
400 - Null Magic Mantle [Magic Resist]
100 - MP + NMM = Chalice Of Harmony [% Mana Regen, Magic Resist]
350 - Boots of Speed [Move]
420 - Dagger [Attack Speed]
150 - BoS + Dagger = Berserks Greaves [Move + Attack Speed]
475 - Regrowth Pendant [Health Regen]
475 - Ruby Crystal [Health]
1150 - Giants Belt [Health]
1100 - Warmogs Armor [Health + Health Regen]
415 - Longsword [Dmg]
1050 - Recurve Bow [Atk Speed]
500 - L +RB = Last Whisper [Dmg + Atk Speed]
-- At this point, it really depends on the situation. Do I need more DPS or more anti-gank?

By the time I B back to get Last Whisper, Warmogs is always fully charged.