Custom Mesh Normals Problem

I am creating a very simple mesh procedurally but I am having problems with setting the normals so I feel like I am miss understanding something. At the moment I am simply making a plane:

 List<Vector3> vertices = new List<Vector3> {
             new Vector3(-width/2,0,-length/2),new Vector3(width/2,0,-length/2),new Vector3(-width/2,0,length/2),new Vector3(width/2,0,length/2)
         };
 
         List<Vector2> UV_MaterialDisplay = new List<Vector2> {
             new Vector2 (0.1f, 0.1f),
             new Vector2 (0.9f, 0.1f),
             new Vector2 (0.1f, 0.9f),
             new Vector2 (0.9f, 0.9f)
         };

 
 triangles.AddRange(new int[]{0, 3, 1});
 triangles.AddRange(new int[]{0, 2, 3});

  List<Vector3> normals = new List<Vector3>();
     for (int i = 0; i < vertices.Count; i++) {
         normals.Add(new Vector3 (0.0f, -1.0f, 0.0f));
     }

 Mesh mesh = new Mesh ();
     transform.GetComponent<MeshFilter> ();

     if(!transform.GetComponent<MeshFilter> () ||  !transform.GetComponent<MeshRenderer> () ) //If you havent got any meshrenderer or filter
     {
         transform.gameObject.AddComponent<MeshFilter>();
         transform.gameObject.AddComponent<MeshRenderer>();
     }

     GetComponent<MeshFilter> ().mesh = mesh;

     mesh.name = "Thing";

     mesh.vertices = vertices.ToArray();
     mesh.SetNormals (normals);

     mesh.triangles = triangles.ToArray();
     mesh.uv = UV_MaterialDisplay.ToArray();

This is correct and draws how I want it to draw except for I can only ever see it from 'above', when i want to see it from below instead, despite having set the normal to be -1.0f for all vertices. I get the same regardless of whether I set it to be -1.0f or 1.0f.