Different levels in the basement

[Tamek]

Hello, (sorry for my English - I use the translator) I am starting to get to know SH3D and the first problem I encountered is as follows. In my basement, the garage is 20 cm below the rest of the rooms. I did "level 0" in the depth of the garage. How can I raise the level of the other rooms in the basement by these 20 cm?

[hansmex]

Make two levels?
On the lower level draw the garage, on the higher level (+20cm) draw the rooms.

H