city engine tv has a lot of example / tutorials..
https://www.youtube.com/user/CityEngineTV
http://desktop.arcgis.com/en/cityengine/latest/tutorials/introduction-to-the-cityengine-tutorials.htm
Maybe there is a problem of content of moisture in the soil that makes buildings and soil very similar, so maybe you should select another Landsat scene from a dry season.
Have you tested with another Landsat scene for your area of interest ?