export sketchup to unity help

im making a city for my game, i need to export my city from sketch up to unity. when i export it as a .obj, .fbx or .3ds it appears but you can only see the default colour and not the colour i have put on the buildings and you can see half the buildings.

when you make the model hit file/export/3d model make it a .fbx file then just drag it in to unity