public class Surface : MonoBehaviour {

    private static readonly GameObject GameObject1 = new GameObject("Surface");

    private static readonly GameObject GameObject2 = (GameObject) Resources.Load("Ground");

    private static readonly BoxCollider BoxCollider = GameObject1.AddComponent<BoxCollider> ();

    private GameObject obj;

    public void Draw() {
        this.obj = Instantiate (Surface.GameObject2, new Vector3 (this.X, this.Y, this.Z), Quaternion.identity) as GameObject;
        this.Add ();
    }

    private void Add() {
        this.obj.transform.parent = Surface.GameObject1.transform;

        Surface.BoxCollider.size = new Vector3 (this.X, this.Y, this.Z);
    }

    public static Surface Create(int x, int z) {
        var surface = Surface.GameObject1.AddComponent<Surface>();
        surface.x = x;
        surface.y = 0;
        surface.z = z;

        return surface;
    }
}

private static readonly Surface[] Surfaces = new Surface[Width * Height];

for (var z = 0; z < Width; z++) {
    for (var x = 0; x < Height; x++) {
        Surfaces[x + z] = Surface.Create(x, z);
        Surfaces[x + z].Draw();
    }
}