I've created new DataGroup properties for Width and Length using the Working Units data type, and while I can manually enter these values I would prefer them to be populated automatically. Is there any way to achieve that?
I then noticed that when using Building Element Info tool > More Info > Details tab you can see the Low and High Range Diagonal values.
I also found that by using the MicroStation Properties tool and expanding the Slab Form entry there are multiple Shapes displayed. By selecting the first Shape and clicking on the Segments icon in the Geometry panel another dialog opens that displays Delta X & Y values.
Is there any way to gather the information from either of these places and include it in a DataGroup Schedule?
Unfortunately there is no "default" solution since Slabs by nature are not defined as rectangular or even four-sided, and therefore do not have Length or Width properties. The only linear quantity property they do include is Perimeter.
It may be possible to extract the Properties dat as described in this 2018 forum thread, using custom Visual Basic code to drill into a cell's structure to extract that data: https://communities.bentley.com/products/programming/microstation_programming/f/microstation-programming---forum/172538/vba-abd-ss6-how-to-get-start-point-and-end-point-of-cell-element/498467#498467
Or, using the CONNECT Edition MicroStation Reports tool you can create a report to extract the low and high range of a Slab Form, and then in Excel extrapolate that data to gather the applicable Length and Width values. This may be a simpler approach and likely the best method for extracting these values from plain Forms using delivered tools.