Hi all, i have a 3 story building with 4 ladders and 6 doors which open/close.
Question is how do i save it as 1 model?
ATM i ‘attach’ the doors and ladders to building so i can move it around in the scene.
I want to reuse this building without having to add the ladders and doors each time. e.g. save as 1 unit but keep functions.
Then that would be a blueprint 
Multiple ways based on your future usage.
1 - Actor BP
2 - Mesh Actor BP (No Event Ticks)
3 - Packed Level Actors
4 - Level Instances
One way at doing it is what @ClockworkOcean has suggested. Using a Blueprint.
You would be able to have all of those assets in your 1 blueprint and then to make it versatile and also removing and adding ladders and doors for each building to change them up a little you would be able to do some simple blueprinting in the construction script to show and hide doors and ladders depending on what you want that building to show and have interactable.