GetTopSurface.cs

public static List<Autodesk.DesignScript.Geometry.Surface> GetTop(Autodesk.DesignScript.Geometry.Geometry geometry)
        {
            List<Autodesk.DesignScript.Geometry.Surface> TopSurface = new List<Autodesk.DesignScript.Geometry.Surface>();
            Autodesk.DesignScript.Geometry.Geometry[] geometries = geometry.Explode();
            foreach (Autodesk.DesignScript.Geometry.Surface g in geometries)
            {
                double d = g.NormalAtParameter(0.5, 0.5).Z;
                if (d>0.1)
                {
                    TopSurface.Add(g);
                }
            }
            return TopSurface;
        }