Shorten up Mesh Generator Class
Im not familiar with XNA or have any experience working with matrixes, vectors and that kind of stuff. But i've made som basic refactorings to make it abit easier to read and maintain.

public static void GenerateCube(float size, out Vector3[] vertices, out Vector2[] texCoords, out Vector3[] normals)
{
        var vertexList   = new List&lt;Vector3&gt;();
        var texCoordList = new List&lt;Vector2&gt;();
        var normalList   = new List&lt;Vector3&gt;();

        const float ninety = (float)(Math.PI / 2);

        for (var i = 0; i &lt;= 2; i++)
        {
            var normal = CreateVector(i);
            var matrix = CreateMatrix(i, ninety);

            var vectorsA = CreateVectorsA();
            var vectorsB = CreateVectorsB();

            vectorsA.ForEach(x =&gt; Vector3.Transform(x, matrix));
            vectorsB.ForEach(x =&gt; Vector3.Transform(x, matrix));

            for (var j = -1; j &lt;= 1; j += 2)
            {
                var vectors = j == -1 ? vectorsA.ToArray() : vectorsB.ToArray();

                var someCalculations = CalculateSomething(j, normal);
                normalList.AddRange(someCalculations);

                AddTextureCoordinates(texCoordList);
                AddVertexes(j, vertexList, vectors);
            }
        }

        vertices  = vertexList.ToArray();
        texCoords = texCoordList.ToArray();
        normals   = normalList.ToArray();

        SetVectorSize(vertices, size);
    }

    private static void SetVectorSize(IList&lt;Vector3&gt; vertices, float size)
    {
        for (var i = 0; i &lt; vertices.Count; i++)
        {
            vertices[i] *= size;
        }
    }

    private static Vector3 CreateVector(int i)
    {
        return i == 0 ? Vector3.UnitZ : (i == 1 ? Vector3.UnitY : Vector3.UnitX);
    }

    private static Matrix4 CreateMatrix(int i, float ninety)
    {
        return i == 0 ? Matrix4.Identity : (i == 1 ? Matrix4.CreateRotationX(ninety) : Matrix4.CreateRotationY(ninety));
    }

    private static void AddVertexes(int j, ICollection&lt;Vector3&gt; vertexList, IList&lt;Vector3&gt; vectorsArray)
    {
        //Triangle 1
        vertexList.Add(vectorsArray[0] * j);
        vertexList.Add(vectorsArray[1] * j);
        vertexList.Add(vectorsArray[2] * j);

        //Triangle 2
        vertexList.Add(vectorsArray[0] * j);
        vertexList.Add(vectorsArray[2] * j);
        vertexList.Add(vectorsArray[3] * j);
    }

    private static void AddTextureCoordinates(ICollection&lt;Vector2&gt; texCoordList)
    {
        //Triangle 1
        texCoordList.Add(new Vector2(0, 0));
        texCoordList.Add(new Vector2(0, 1));
        texCoordList.Add(new Vector2(1, 1));

        //Triangle 2
        texCoordList.Add(new Vector2(0, 0));
        texCoordList.Add(new Vector2(1, 1));
        texCoordList.Add(new Vector2(1, 0));
    }

    private static IEnumerable&lt;Vector3&gt; CalculateSomething(int j, Vector3 normal)
    {
        var someCalculation = normal * j;
        return Enumerable.Repeat(someCalculation, 6);
    }

    private static List&lt;Vector3&gt; CreateVectorsB()
    {
        return new List&lt;Vector3&gt;
                   {
                       new Vector3(-1, -1, 1),
                       new Vector3(1, -1, 1),
                       new Vector3(1, 1, 1),
                       new Vector3(-1, 1, 1)
                   };
    }

    private static List&lt;Vector3&gt; CreateVectorsA()
    {
        return new List&lt;Vector3&gt;
                   {
                       new Vector3(-1, -1, 1),
                       new Vector3(-1, 1, 1),
                       new Vector3(1, 1, 1),
                       new Vector3(1, -1, 1)
                   };
    }