I’m not sure if this should be under lighting or rendering, but since the problem can be seen even before rendering so I guess it falls under this forum.
For some reason, certain faces seem to be shaded awkwardly. This is especially so for those faces which I had to add myself instead of using subdivisions/extrusions/etc. Only one light source used (sun type) for this one as I’m still feeling my way around lighting.
You’re using gourad shading on a mesh with hardly any vertices, is it any surprise? Either sub-divide the mesh or turn it back to flat shading, which is what you’d be better off with. Also, it looks like you have some bad normals, select the trouble faces and press ctrl+n
