Setting Up an Under Construction Page
Install and configure an "Under Construction" page in Wordpress using one of two methods: a simple setup and configuration method, or an advanced method that offers more configuration options.
Simple method
This Under Construction page is simple to install and configure via WordPress but offers few options to add to the template.
Steps
Install WordPress. See KBA: Installing Wordpress
In the Plesk Panel, click WordPress

Under the site in question, click the radio button to enable Maintenance Mode

The default Maintenance Mode looks like this

To change options, click the Setup link under Maintenance Mode

Here are the options that can be configured

Click the OK button when finished

Advanced method
This method uses a default open source Under Construction page. While it is more complicated to install, it does offer more configurable options.
Steps
Go to the BlackrockDigital GitHub website
Click the Clone or download button, then click on the Download Zip

In your Plesk Panel click on the Files button

Click the Upload button and upload the startbootstrap-coming-soon zip file

In the Plesk File Manager, select the file and click Extract Files

Extract the files into the current directory

Enter the startbootstrap-coming-soon-master directory

Select all of the files by clicking the checkbox next to Name

Click the Move button

Select the directory where your website resides (httpdocs in most cases)

Click the up arrow to go up to that directory

Select the folder and the zip file that contained the files

Click the Remove button to delete those file/folders

This is the default option for the Under Construction page

In the Plesk File Manager, you can edit the index.html to change options

Be sure to click the OK button to commit your changes
