Kalista build question

Usually I build Runaans -> Greaves -> BT -> IE/LW -> defensive/AS Item (situational)

I see people building Bork on Kalista but I don't know at what point I should build it. It's effective against tanks I understand but Runaans is extremely helpful to me because I can push waves / cs much easily. Greaves for jumping distance ofc. And BT's life steal helps me kite very efficiently. Combine BT with Runaans and suppose a fight is to break out on a lane by minions I replenish my health effectively while in battle.

at which point does one build Bork on kalista? Because after BT I can just go LW and it helps me shred tanks as well.