It’s a great idea to use a “maintenance mode” page to temporarily take your site offline and display a notification to your visitors. It’s also smart to use a maintenance mode or “coming soon” page while you’re building a new website. You’ll want to use a plugin that will display a notification page for visitors, while still allowing administrators (you) to access the admin area and the full website.
Our favorite plugin for this is the Coming Soon Page Pro plugin.
But you might also check out the WP Maintenance Mode plugin for comparison.
Hope this helps!