To create new buildings and floors, please go:
In VisioMapEditor / Settings / Properties / Buildings / Edit.
Then you chose the building you want and click on Floors / Edit.
UL = Upper Level
LL = Lower Level = for underground floors = negative altitude
Check this Blog : Map Design Guide – Multi-building
Don’t forget to match the altitudes here with the ones from your geo-localisation provider.
Also the floor default thickness should be set as : How to update floor altitudes