Hello Andreas,
Thank you for your question. The right tab under Reports section is for the rooms. If the model (IFC or Revit model) has the "Space" element, then the reports will show the calculation of the space's area in the model and show how much room is inside it.
We have reviewing this feature and it appeared that the functionality is currently broken. We will file a bug for this issue and keep you updated when issue has been resolved. We apologize for the inconvenience this may have caused.
Best Regards,
Fern Udomrasami