3D buildings on Google Earth

[ErikJan]

Does anyone know how one can get 3D buildings created and then displayed on Google Earth for everyone to see?
I think Google is doing many public buildings/structures themselves, I do see some residential buildings in some cities too however. Sometimes only one or two, which makes me think someone must have either requested that or created that and then submitted it to Google.
I searched the net but don't seem to be able to get a simple explanation.
I'd also guess that if one would make pictures from different angles, automatically building a 3D representation shouldn't be terribly complex.