how to allow the user to write where he want to save the selected files in c#

rivate string GetFilename(string file)
        {
            int length = file.Length - (file.LastIndexOf("\\") + 1) - 4;
            return file.Substring(file.LastIndexOf("\\") + 1, length);

        }

        private string GetExtension(string file)
        {
            return file.Substring(file.LastIndexOf(".") + 1);

        }

        private void MsbuildGeneratorBtn_Click(object sender, EventArgs e)
        {
            GenerateMSBuildFile();

            if (folderBrowserDialog1.ShowDialog() == DialogResult.OK)
            {
                this.textBox1.Text = folderBrowserDialog1.SelectedPath;
            }



            
        }

        private void GenerateMSBuildFile()
        {
            List<ProjectFile> projectList = new List<ProjectFile>();
            


            //WriteBuildFileHeader();

            // Add all of the selected files to the template.
            foreach (var projectFile in projectFileList)
            {
                if (projectFile.IsSelected == true)
                {
                    Console.WriteLine(projectFile);
                    projectList.Add(projectFile);
                    //WriteItem(projectFile.FullPath, "C:\\");


                }

            }