An elevator, which is equipped with command blocks. These teleport the player to the desired floor.

The idea is probably not particularly unknown but since I have not found you here I just post it:
An elevator which teleports you with command blocks to a certain floor. If you have understood the principle, it is not difficult to build. But can be, depending on the size, very time consuming.
Not suitable for survival as you can't craft command blocks.

Instructions:

First you build the elevator cabin. The size does not matter but you must be careful that you do not place command blocks next to each other. The buttons I would place on the command block because it can come (depending on how you have built your room) that the button controls two different command blocks.

When you have finished your room, build the exact same room on top of your first room. Repeat this as often as you like, depending on how many floors your house/hotel/shopping mall etc. has.
To set the commands for the command blocks press F3 because you need your coordinates. Best is to stand in front of the command block and ''open'' it with a right click. Now enter: /tp @p x y z
at x and z you enter your x and z coordinates and at y the coordinate the room above you has.

Since probably no one has understood the description here is an example :P:

An elevator car is 4 blocks high with the ceiling. You are on the ground floor:
Your coordinates when standing in front of the KB for 1st floor: x10 y20 z30
Your coordinates when standing in front of the KB for 6th floor: x15 y20 z12
Command for KB 1st floor: /tp @p x10 y24 z20
Command for KB 6th floor: /tp @p x15 y44 z12

Hope that was somehow understandable :)
But I think many of you get it done without instructions :)

Ps: If you do not know how to get command blocks then read it here ;)
You enter in the chat: /give EUER_SPIELERNAME 137 5
137 is the data value of the block and 5 is the count.