Sometimes, You need to make changes to your website’s design, WordPress theme or content. This would make your website temporarily unavailable to public access. In this case you will probably need make your website look and feel more professional.
There are many free plugins on WordPress.org that let you put your website into maintenance mode and display a custom message to your visitors. For example: WP Maintenance Mode (by Designmodo). WP Maintenance Mode allows you to have full access of your website during the maintenance mode.
Plugin WP Maintenance Mode: