Did you ever ask yourself how the 3D buildings in GoogleEarth are made? It’s done with Google’s free tool SketchUp. It’s an easy to use ( all is easy, if you know how it works 😉 ) 3D modeling software. You can learn it in a few hours and design complex buildings. Just leave the Window “Instructor” open (get it with Menu–>Window–>Instructor), and it shows you for every tool how it can be used. This helps enormously.
Sketchup 7 works fine with the latest version of wine (wine-1.1.18) and a Unbuntu 8.10 (Intrepid Ibex). You just have to circumvent a few quirks described here.
The default Ubuntu repository uses an pretty old version, and SketchUp crashes all way long. Actually it’s not usable. Therefor you have to use the latest repository from WineHQ:

# wine
deb http://wine.budgetdedicated.com/apt intrepid main #WineHQ - Ubuntu 8.10 "Intrepid Ibex"

Sometimes key-presses on the keyboard and mouse clicks doesn’t work, or the action happens one click/press delayed, and I couldn’t find a workaround, but as the graphic shows, I’ve been able to create a more or less complex church. It’s a Catholic church St. Peter und Paul in Weil der Stadt. You can download this model from Google’s 3D Warehouse or here [<1MB].
I don’t know if the church will be added to Google Earth’s 3D buildings, but you can download the model and load it into SketchUp 7 on a Linux system, but it need Windows if you want to see this 3D model also in GoogleEarth, because SketchUp running with Wine doesn’t recognize a running GoogleEarth instance on Linux.

On Windows system start GoogleEarth, then start SketchUp and load the model. Afterwards press the button “Place Model” in the icon menu.
This make the model appear in Google Earth, and it’s added to “My Places” on the left side in your menu. Now you can use it as if the building was downloaded online like the regular 3D buildings.
I didn’t find a way to bring this 3D model into GoogleEarth on Linux. Anyway. I don’t need this feature badly, but if anyone has a solution, I would be glad about a comment.