Roof polygons from LoD2.2

Dear colleagues,
sorry for writing in english as my current level of dutch does not allow me to write such message.
I would be interested in the Lod2.2 datasets of all buildings in the NL to study the potential for food production on flat roofs (rooftop farming). The dataset seems very informative for that but I have downloaded loaded the LoD2.2 dataset from the TUDelft WFS on QGIS but it does not display all the polygons only some 18.000. Additionally, we have downloaded the full data (the 35GB) but it contains only .dat files. Would it be another way of displaying the full dataset from the WFS or eventually translate the .dat to a shapefile with your tools ?

I would like to thank you very much in advance for your help on that !
Best regards,

WFS is not meant for downloading such large amounts of data. Better go for the full country PostgreSQL dump over here: 3D BAG Viewer