Pass in your Google Analytics Profile Id and use GA Reporting API to get information and output to spreadsheet.

runReport.appscript.js

function runReport(profileId) {
  var today = new Date();
  var oneWeekAgo = new Date(today.getTime() - 30 * 24 * 60 * 60 * 1000);

  var startDate = Utilities.formatDate(oneWeekAgo, Session.getScriptTimeZone(),
      'yyyy-MM-dd');
  var endDate = Utilities.formatDate(today, Session.getScriptTimeZone(),
      'yyyy-MM-dd');

  var tableId  = 'ga:' + profileId;
  var metric = 'ga:visits';
  var options = {
    'dimensions': 'ga:medium,ga:source',
    'sort': '-ga:visits,ga:source',
    'max-results': 25
  };
  var report = Analytics.Data.Ga.get(tableId, startDate, endDate, metric,
      options);

  if (report.rows) {
    var spreadsheet = SpreadsheetApp.getActiveSpreadsheet();
    var sheet = spreadsheet.getActiveSheet();

    // Append the headers.
    var headers = report.columnHeaders.map(function(columnHeader) {
      return columnHeader.name;
    });
    sheet.appendRow(headers);

    // Append the results.
    sheet.getRange(2, 1, report.rows.length, headers.length)
        .setValues(report.rows);

    Logger.log('Report spreadsheet created: %s',
        spreadsheet.getUrl());
  } else {
    Logger.log('No rows returned.');
  }
}