GetOrCreateSharedParamsFile.cs

/// <summary>
        /// Get or Create Shared Params File
        /// </summary>
        /// <param name="app"></param>
        /// <returns></returns>
        public static DefinitionFile GetOrCreateSharedParamsFile(Autodesk.Revit.ApplicationServices.Application app)
        {
            string fileName = string.Empty;
            try // generic
            {
                // Get file
                fileName = app.SharedParametersFilename;
                // Create file if not set yet (ie after Revit installed and no Shared params used so far)
                if (string.Empty == fileName)
                {
                    fileName = Microsoft.VisualBasic.FileIO.SpecialDirectories.MyDocuments + "\\MyRevitSharedParams.txt";
                    StreamWriter stream = new StreamWriter(fileName);
                    stream.Close();
                    app.SharedParametersFilename = fileName;
                }
                return app.OpenSharedParameterFile();
            }
            catch(Exception ex)
            {
                MessageBox.Show("ERROR: Failed to get or create Shared Params File: " + ex.Message);
                return null;
            }
        }