IsHorizontal.cs

 public static bool IsHorizontal(this Line Line)
        {
            double TOLERANCE = 0.0000001;
            XYZ p1 = Line.GetEndPoint(0);
            XYZ p2 = Line.GetEndPoint(1);
            return Math.Abs(p1.Y - p2.Y) < TOLERANCE;
        }
       

IsVertical.cs

 public static bool IsVertical(this Line Line)
        {
            double TOLERANCE = 0.0000001;
            XYZ p1 = Line.GetEndPoint(0);
            XYZ p2 = Line.GetEndPoint(1);
            return Math.Abs(p1.X - p2.X) < TOLERANCE;
        }