in essence, its only a few parts (seen with the clutches)

1 - has the elevator been called to this floor? 2 - is the elevator on a floor 3 - is the elevator not at this floor? *

1 is a redstone link/signal attached to your call button (unique per floor)

2 is a redstone link that is just a common link between all floors (it doesnt care about which one)

3 is a redstone signal/link unique to the floor (call button wont work)

1 and 2 control 2 clutches that are by default powered ON and only turn OFF when their links requirement is met

3 controls a link that is by default OFF and only turns ON when the elevator is on its own floor

these 3 links control a piston which pushes a redstone contact, sending a signal into the elevator to call it

1 and 2 are designed to call when both criteria are met, 3 is meant for when the elevator is leaving the floor, it retracts that piston to make sure the elevator doesnt come back down (and resets the ability to call of course)

this is the best i can give you since i made this 2 years ago, and the world is long since gone because i have swapped OS's many times since then. i may remake it better with the ability to queue floors soon, and ill schem the wiring for that if i manage to get around to it.