The property lists displayed in the Floor Manager UI for the Project, Site, Building and Floor items are populated by DataGroup Catalog Items. These are stored in the 'Default' items found in the Architectural 'Buildings' and 'Floors' Catalog Types. These Catalog Types should only be used for this purpose. For instance, floor elements, i.e. slabs should be created under the slab catalog type.
An example of how this works is that the DataGroup Floors item is used to populate properties in Floor Manager, e.g. Approx length/Width, here I have modified the dimensions from the defaults, the new floor I then created has picked up those values:
There is a similar item under Buildings. A property added to either item will show up in the Floor Manager so things can be added, for instance I just added this dropdown list of UK Listed Building grades:
This was added by creating a new DataGroup Definition containing this pop-down list:
that was then added to the Buildings > Default Item:
I have found that some properties behave slightly differently within the Floor Manager UI, the Hidden checkbox in the DataGroup Item does not hide the property from the UI (although as there would be no point whatsoever in creating a new property then hiding it!) and the default item in a list does not seem to apply which is a fairly minor issue as these properties are only set once per project.