Why does my model look "patchy" after I enable smooth shading on it? [![enter image description here][2]][2]

How I do I fix those strange patches? I tried hours of subdividing areas and such but to no luck.. Is there a simple fix? Could someone people help, I'd be glad to share the Blender file I just really need to get this finished as soon as possible. 

Blender file, would be amazing if you could help :)
The normals appear to be inverted in those areas. In edit mode, select the whole mesh (A key) and then recalculate the normals by pressing Ctrl + N (or using the menus: Mesh > Normals > Recalculate Outside).