If you are looking for fast method to post maintenance mode message on your wordpress blog than you must try Maintanence Mode wordpress plugin .
This Plugin helps you to add a maintenance mode message page on your blog that lets visitors know your blog is down for maintenance time . Best part of this plugin is that it will save your time and you can post a maintenance mode alert by just activating this plugin in few seconds only .
Adds a maintenance-page to your blog that lets visitors know your blog is down for maintenancetime. User with rights for theme-options get full access to the blog including the frontend.
Activate the plugin and your blog is in maintenance-mode, works and see the frontend.
This free plugin allows you to choose from several pre-designed pages to be your WordPress blog’s temporary landing page while you’re doing any edits that you want to hide from the world.
Visitors who come to your blog when the plugin is activated land on your chosen “under construction” page, which you can customize with your own messages and in multiple languages.
If you are a good graphic designer than you can add your own stylesheet and add the url of this style to the options of the plugin . But if you don’t want to create new designs than also you can try other cool designs provided by plugin developers.