Hello GarflD,
I downloaded your .fbx and tried to import that into UE4. I received an error message saying that there were not triangles. I then imported that .fbx into Maya. That imported your building and I was able to view it. I then exported that from Maya and into UE4. I was able to import it there with out issue.
I believe this could be a workflow issue from Blender to UE4.
Have a look at this documentation.
If after looking through this there is still an issue I will continue to investigate this issue at that time.