After some data conversion voodoo I got the data from DXF into Blender 3D.
In Blender I cleaned the data, then exported FBX to Marmoset. Since the roof data is not very clean, lots of fog helped creating a misterious mood.
The performance in Blender and in Marmoset is really good.
I now try to get the data into Unreal engine and export an AR application.