Beginner importing houses from Sketchup help!

I have created a number of streets in Sketchup pro (using google maps to get the houses in the right position) which I now need to import into unity. I'm a Unity beginner and going slightly mad already! When I import the houses (which contain solid shapes and photo textures) only the textures seem to import in. I'm probably doing something basic wrong but any advice on this would be gratefully received. Also about the best way to create the town in Unity. Thanks.

In sketchup click Export 3d model in the file menu, at the bottom right corner there is an options button click it and select 2 sided. click ok and export As 3DS

Have you tried reversing the surface normals before you import them?