// Creating the property.
private RuntimeBuilder _RuntimeBuilder { get; set; }

// Initialize the RuntimeBuilder.
_RuntimeBuilder = new RuntimeBuilder(
                Path.Combine(Application.StartupPath, "working"),           // working directory
                Path.Combine(Application.StartupPath, "working", "obj"),    // intermediate directory
                Path.Combine(Application.StartupPath, "Content"),           // output directory
                TargetPlatform.Windows,                                     // target platform
                GraphicsProfile.Reach,                                      // graphics profile
                true)                                                       // compress the content
            {
                Logger = new StringBuilderLogger()                          // logger
            };
            
// Pick Files & Build Content.
private async void ButtonPickFiles_Click(object sender, System.EventArgs e)
{
    if (openFileDialog.ShowDialog() == DialogResult.OK)
    {
        await _RuntimeBuilder.BuildContent(openFileDialog.FileNames);
    }
}