Please help me understand your case,
- Is there only one elevator working in all four floors?
To model a lift, make use of a Tablefile/ list to update the Parts which needs to be elivated with From location (Floor number), To location (Floor number).
Then asign the task to the elevator to transport these parts to the respective location & delete the row from the Table.
Please make use of CrossSlidingCar object available in PlantSim.
View the PlantSim example model with category: Continuous material flow & Topic: CrossSlidingCar