Incorrect roof elevation in KML

[veriandi]

Hello,
I am trying to convert a building only CityGML model into KML using 3dcitydb for visualization purposes. I stumble upon a problem where the roof surfaces doesn't "start" at the right elevation. It starts at the ground, the same elevation as the base of the building.

I use EPSG:32748 (UTM 48S) for the 2D coordinates as well as for the height.

I'm at my wits end, can you please shed some light on the issue?

I'm also open if you need any further information on the data that I'm using. Thank you!