Plane model don't have 2side material

Turn on backface culling in maya to get a sense of what your model is going to look like in Unity. Since game developers don't have near limitless resources for rendering like animated movies do, we have to deal with normals determining which side of a face gets rendered. If you're really intent on having 2-sided faces, you can write a shader with 'cull off' in the culling instructions but realize that this makes your model twice as taxing on the system as it was before.

A better solution is to go through your model in maya and make sure all of the normals are pointing outwards. If you go to display > polygons > face normals you will get little lines that point in the direction your face points. You can also go to display > polygons > backface culling to turn off backface culling and see which faces need to be repaired. You can also try going to normals > conform normals, although I've had spotty luck with this function.