I want to do a level that sets the floor level to 0.

[LeeJaeYoung]

This is a structural drawing of the roof on the first basement floor.
I would like to display the level based on the roof of the first basement floor.
-1500 => 0
-800 => +700
I want to do it like this.

If you can create a new level with GDL, please let me know.

[LeeJaeYoung]

sorry.
You need to use Elevation Label 25.

[Laszlo Nagy]

You should read about Reference Levels in the Archicad Help.

You can specify a value for the 1st Reference Level or 2nd Reference Level in the Options > Project Preferences > Reference Levels Dialog. Then, when you place a Level Dimension, you can specify that the Level Dimensions displays its values relative to the 1st/2nd Reference Level, not the Project Zero.