And now to make that you can make a simple way to create under construction page
Here codes you can use in config main /protected/config/main.php. This trick does when you create empty file called underconstruction.txt in your root website.
return array( 'basePath'=>dirname(__FILE__).DIRECTORY_SEPARATOR.'..', 'name'=>'Your Site', 'sourceLanguage' =>'en_US', 'language' =>'en_US', 'catchAllRequest' => (file_exists(dirname(__FILE__).'/../../underconstruction.txt')) ? die('<div style="text-align:center;line-height:300px;font-size:100px;>Under Construction</div>'): null,
That's code check all request to your yii site whether the file underconstruction.txt is exist or not in your root web directory. If it exist and then your website is under construction and view the message you have supply