Sivir is a bit of an oddity in the ADC role where she's like an AD caster ADC kinda like ezreal/corki but not to that extent so shes still a bit more AA reliant than those 2 but can spam Qs.
BT first on anyone is definitely not recommended.
She was my first ADC and my comfort pick when I'm forced to solo Q with her bc I dont know how reliable the support will be, and have tried a lot of diff builds. So far liking this:
- Rush BF sword
- Vamp scepter for sustain, spell shield should be enough for mana now
- Zerker boots, essence reaver
- Avarice blade, zeal
- Sheen/Phage to finish tri force
- Last whisper/ghostblade/BotRK/IE/GA as needed
With the essence reaver + avarice blade combo you can QW to clear entire waves without worrying much about mana. This frees up your support to go roam - you clear wave then can roam as well if needed nearing the end of the laning phase. During laning phase w reaver you can spam pokes and Ws will bounce off their waves adding additional damage to the enemy if they try to stay to last hit. Usually their waves will stay shoved at their tower. Very aggressive play w sivir to shove down their turret early allowing bot to roam. Spellshield makes it very hard to get picks & ganks on her when used properly
Avarice blade I keep for quite awhile and lets me ramp up gold quickly with super waveclear to pick up all the CS and even more gold on some jungle camps in between roaming. Reaver will keep her mana & HP sustained.
Tri force gives her huge burst then rundown enemy champs with passive & ult (+tri force move speed) makes her very hard to get away from. Roaming w sivir is pretty strong too with her ult --> ganks. Tri force can be obtained fairly quick here with avarice blade giving extra gold giving a huge power spike much earlier. Games usually will end here for me
Armor pen is usually picked up next, then any of the items in 6. based on what the enemy comp is.
Compared to standard IE to PD builds, I have mana issues and dont want to use spellshield JUST to get mana and would save it to deny CC/ganks and make trades more favorable by blocking skillshots, but NOT trying to bait a skillshot just for mana since that can bait me into getting ganked. Damage also seems to be higher with more abilities being able to be spammed along with empowered spellblade procs from low CD Qs, AA resets on W, + spellblade empowered attack when charging in on R