https://www.teamviewer.com/en-us/ is like a remote assistance thing
Anyway the difficulty of this really depends on how fancy you want the elevator to be. If you're okay with having simple up and down buttons that take you up or down one floor at a time, that will be comparatively easy. Implementing floor number buttons will however be extremely complicated, especially if you want to implement standard elevator logic like stacked calls (although I guess that's probably overkill for a singleplayer map). Also, if you have any method to get between floors in your map without the use of the elevator you would need call buttons on each floor which will be fairly complex.
There are also limits to the number of entities you can put in the map and events count toward this limit, as do item pickups, clutter objects, etc... Anything more than simple up/down buttons could easily take 100-200+ events.
If you are okay with up/down buttons, here is where I would start.
X--1-----2-----3-----4-----5--Y
X is a starting keyframe slightly below the first floor.
1-5 are keyframes at each floor.
Y is an ending keyframe slightly above the highest floor.
The mover should be either pingpong infinite or loop infinite and there should be a trigger auto to start it moving as soon as the map loads.
The keyframe at each floor should have Trigger Event With UID linked to a Delay with 0 delay on it, then to a Mover_Pause, then back to the gold keyframe. From this delay you can also link to something to (for example) open the elevator doors.
The up/down buttons inside the elevator car will have to go to a Reverse_Mover to set the direction of movement, and then to an invert->mover_pause to get the car moving again.
You will also need to have special handling for when the player is on the 1st floor so they can't command the elevator to go down, and the reverse for the top floor. The use of goals may be necessary for this. The last keyframe Y is there to stop the movement direction from automatically reversing at the end of the run
I'm most familiar with multiplayer mapping and in MP this would require hardcore use of "keyframe tricks" to allow triggers to activate events directly. I'm not sure what's involved with getting triggers->events working in SP. Maybe you can just link them and it will work