Actually, there is a relatively new feature called Get Map Data in CityEngine 2016.0 and 2016.1 (the two most recent versions). This allows you to create 3D city models quickly and easily from OSM data. Maybe this tool will work for your needs? You can select a region on a map, and it automatically downloads the basemap, elevation data, and OSM data (building footprints and/or street networks) and aligns it all. In 2016.1, there is a rule already assigned to the footprints, so you can just select them all and generate.
File -> Get Map Data
search for your city -> select a region on the map
choose a basemap
check the box to download elevation data (if you want it - needs arcgis organizational account)
check the box(es) to download OSM data (polygons for building footprints, networks for streets)
select all building polygons -> generate
Check out the help page for more detailed instructions:
Get map data from ArcGIS Online / Portal