A) After scaling models down, walls can end up very thin. They usually need to be thickened using the Solid by Extrusion or Modify Solid tools.
B) Elements on the inside of buildings can be removed if they are not intended to be in the printed model. This can be done easily by turning off the layers that contain them, or by using Subtract Solids to hollow out the building.
C) Some details on buildings, such as door and window frames, end up being too small after the model is scaled. These details need to be simplified into thicker shapes or removed from the model.
The picture below shows the printed building model.