Hello guys, as the title says, i have this problem, what to do?
What format?
.fbx usually, is this the problem? I found the settings from unity to import the materials but it doesnt always work. The problem with thr faces still remains.
@Azaroth: “missing faces” often happen because there are problems with the normals. Make sure you have them all pointing correctly.
cheers, gryff 
Thank you gryff, but how can i check it? 
In Maya, go into the Display menu> Polygons and choose “Face Normals”. This will show you the direction your polygons pointing at.
The ones you don’t see, probably pointing into your model. Unity doesn’t draw the back of polygons. But 3d apps doing that. That’s why Unity does not show them.
To fix that in Maya, go into the Normals menu and choose “Conform”. Or select each face with the wrong direction and choose “Reverse” under the normals menu.
Sweet! It worked, thank you very much!!!