Fix your Normals on your Mesh. Alternativly use a doublesided Material but it will Cost you more Performance. Google up how todo this in Maya since I dont own Maya (Modo user)
Side tip: Dont use N-Gons. Game Engines only support triangulated Meshes.
Please don’t use answers to thank somebody, the answer part is only meant for answers to the question. Press the button under the down arrow instead to mark the question as answered.