You have a few different options for running CityGen. First of all, You can create "floor plan" polygons in the FG layer, from which CityGen will grow your buildings - even splines created with the sketch tool will do. Or, you can have a bigger mesh (i.e. ground), and select some polygons from it  - and let CityGen do it's job on them. Or, finally, you can run CityGen with an empty foreground layer, and it will create a random city block for you.

When creating the floor plans, it's almost imperative that you work in real world scale!!

After you have chosen which of the above methods you wish to use, run the script. Depending on what you have in the FG layer, you may be prompted with quite self-explanatory requesters (no need to go in-depth with them here)... after those, following requester will appear.

This is the first of the four tabs in CityGen. Let's review the settings:

1. Buildings surface base name

During the building creation process, CityGen will create various new surfaces. This string works as the base of the surface names. Using the default "Building", you may have surfaces like Building_0001_Roof_Edge or Building_0003_Window_Frames etc.

2. Numbered surfaces

"All (per building)" will give numbered surfaces to each house - i.e. "Building_0003_Window_Frames" would be the surface for the window frames in the 3rd building. "Random" will also give numbered surfaces, but distribute them between the buildings. So, "Building_0003_Window_Frames" can appear randomly in any of the buildings, regardless of the order in which the buildings were created. "Off" will skip the step which assigns these numbers to surfaces.

3. Random name limit

You can limit the amount of numbered surfaces with this setting, in order to avoid having potentially hundreds of separate surfaces in the model. If this setting is set to i.e. 3, there will be three different roof, window etc. surfaces in the model. This setting only works when numbered surfaces is set to random.

4. Per poly window names

Activating this will give different, randomly numbered surfaces to each window polygon. It's great for i.e. having some of the windows lit in night time scenes, but there's a drawback: Assigning the surface names can take a near-infinite amount of time, so be cautious when using this setting.

5. Optimize original geometry

This setting is used to avoid excess amounts of geometry, as well as ugly looking widows. There are a few options, but usually you will get best results when this is set to "Both". If you don't get the floorplan you want this way, experiment with the other settings.

6. Optimize amount

This setting is used to determine how "rough" the optimized mesh will be. In practice, it controls the size of smallest allowed detail in X and Z axises.

7. Optimize final geometry

When this setting is active, some simple point merging etc. optimizing will take place when the city has been built.

8. Force positive Y axis

This will make your buildings always grow up. If not activated, the buildings will grow to the direction of the poly normals of the original "floor plan" polygons.

The second tab controls the floors:

9. Floors Min / Max

The buildings created by CityGen will have a random number of floors between these two values. If you want all buildings to have  *exactly* 5 floors, set both to 5.

10. Floor height

This is, as the label says, the height of the floors in your buildings. The +/- setting randomizes this between buildings - within one building, the floors are always of the same height.

11. Ground floor

This setting will create a simple ground floor to your buildings.

12. Alternate floor

"Normal" floors in Citygen have windows. You can use this setting to make every 2nd floor to be either empty, or have a simple balcony.

The next tab controls the roof appearance:

13. Roof edge

This setting will create an edge for the roof. The randomness option can be used to have variation between buildings.

14. Roof bevel

Use this option to create beveled roofs. Same issues that cause problems with regular lightwave bevels may be problematic with this setting too - i.e. concave shapes may cause the bevel operation go cattiwompus.

15. Roof nurnies

Selecting this option will create random antennae, ventilation shafts etc. to the tops of the roofs. As the placement of these elements is controlled with the bounding box of the roof polygon, some of the nurnies may levitate in mid air if the house is oddly shaped (sorry ;-). Nurnie limit sets the highest number of nurnies that may be applied to any of the rooftops.

The final tab is used to set up the appearance of the windows.

16. Windows

Use this to randomize windows between buildings, or to force all buildings to have windows.

17. Window size (% of floor height)

This setting controls how big percentage of the building is covered with windows. Set it to high valies for skyscrapers, low values for old factory buildings etc.

18. Inset (& of window size)

This setting controls how deep the windows are insetted in the wall. For some modern buildings, even a radical setting of 0 may look good...

19. Window frames

Most of the time 3D window frames tend to be the best looking. But, when you start calculating the amount of windows in a city, you may sometimes need to reduce this setting to keep the polycount bearable.

20. Window frame cross

Use this to apply crossbars on the windows

21. Reset settings

Last but not least, there's this button that's visible at all times... check it when your cities start to look TOO futuristic (or impressionistic ;-) but you don't know what causes the problem...

For technical help (Also for ModPak users!!), there is also a mailing list for the PlugPak users.