You can use sketchup to make some simple or very complex shapes for buildings, extrude the shape to get some height if you want and then use this ruby script, roof.rb to add a variety of roof styles, the site has alot of scripts, the roof.rb is the most recent roof generator though.
Its simple to use, just select the face you want to put a roof on, for hip and mansard style, click your plugins menu item at the top and then roof.rb, then make your choice of style and settings.
For the other styles you open roof.rb first via the plugins menu and then click on three points to set where your roof will be built on the shape. you can texture the whole thing,eaves and all in one color with the paint bucket fill
or do the following for more control
Roof.rb builds the roofs as groups or components, so they have to be exploded first. To do that you select the roof and a blue box will appear, then go edit and select the bottom item,,,,,model instance something or other, click on that and then select explode, now you can texture your roof as you want.

Simply put the script in Sketchups plugin folder, oh yeah, some scripts are zips with documentation, some are just a text page which you save as whatever its name is+.rb


Then just render topdown views and gimp them into brushes.
SeerBlue