KML example

using System.Xml.Serialization;

namespace CreateKmlFromFiles
{
  public class KmlModel
  {
    [XmlRoot("kml", Namespace = "http://www.opengis.net/kml/2.2")]
    public class Kml
    {
      public Document Document { get; set; }
    }

    public class Document
    {
      public string name { get; set; }

      public string description { get; set; }

      public Style Style { get; set; }

      public Placemark Placemark { get; set; }
    }

    public class Style
    {
      [XmlAttribute("id")]
      public string id { get; set; }

      public LineStyle LineStyle { get; set; }
      public PolyStyle PolyStyle { get; set; }
    }

    public class LineStyle
    {
      public string color { get; set; }
      public string width { get; set; }
    }

    public class PolyStyle
    {
      public string color { get; set; }
    }

    public class Placemark
    {
      public string name { get; set; }
      public string description { get; set; }
      public string styleUrl { get; set; }
      public LineString LineString { get; set; }
    }

    public class LineString
    {
      public string extrude { get; set; }
      public string tessellate { get; set; }
      public string altitudeMode { get; set; }
      public string coordinates { get; set; }
    }
  }
}

using System;
using System.IO;
using System.Text;
using System.Xml.Serialization;

namespace CreateKmlFromFiles
{
  class Program
  {
    static void Main(string[] args)
    {
      StringBuilder sb = new StringBuilder();
      sb.Append("7.0971881, 50.7359953, 2357");

      KmlModel.Kml kmlModel = new KmlModel.Kml
      {
        Document = new KmlModel.Document
        {
          name = "Paths"
          , description = "test"
          , Style = new KmlModel.Style
          {
            id = "red"
            , LineStyle = new KmlModel.LineStyle
            {
              color = "7f0000ff"
              , width = "4"
            }
            , PolyStyle = new KmlModel.PolyStyle
            {
              color = "7f0000ff"
            }
          }
          , Placemark = new KmlModel.Placemark
          {
            name = "Absolute Extruded"
            , description = "Transparent green wall with yellow outlines"
            , styleUrl = "#yellowLineGreenPoly"
            , LineString = new KmlModel.LineString
            {
              extrude = "1"
              , tessellate = "1"
              , altitudeMode = "absolute"
              , coordinates = sb.ToString()
            }
          }
        }
      };

      TextWriter txtWriter = new StreamWriter
      (
        Path.ChangeExtension
        (
          System.Reflection.Assembly.GetEntryAssembly().Location
          , ".kml"
        ));

      XmlSerializerNamespaces ns = new XmlSerializerNamespaces();

      ns.Add("", "http://www.opengis.net/kml/2.2");

      XmlSerializer xmlSerializer = new XmlSerializer(typeof(KmlModel.Kml));
      xmlSerializer.Serialize(txtWriter, kmlModel, ns);

      txtWriter.Close();
    }
  }
}