I forgot to share this. Some already know it and are using it?
It is a feature that can be useful; for instance, in looking for missing walls...
Go to the "Project Properties" Dialog box, "3-D View Details" tab: on the list of "Components to View", uncheck which ever might you want, specially roofs, floors, exterior walls, ceilings. You can then see the interior of your building as never before.
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Demba NDIAYE