I have idea to make the multilayer in the game world to make mine and undergound laborotories and etc. Thats all my idea :)
This has been discussed a few times before.
Here is Tynan's answer about the matter.
Multilayer is referred to as z-levels within these types of games. Hope this helps out.
Question: Will there be z-levels (vertical mapping)?
Answer: All the coordinates are tracked in 3-vectors already (though only the two horizontal axes are used), so the potential for 3D is in the game.
I am afraid that there is basically no way a modder would ever be able to mod Z-axis into the game. It is a beast of a feature. Here's some basic issues you'd have to handle:
-Pathfinding
-Lighting spilling over Z-levels
-Save/load of a geometrically larger amount of stuff (e.g. 200x200 map = 40k squares, 200x200x10 = 400k squares!)
-Line of sight for shooting
-AI tactical analysis of shooting lines of sight etc
-Cover usefullness varying at vertical angles
-Interface for moving through Z-levels
-Rendering visible lower Z-levels while being on higher ones