Somentra offers a custom Maintenance mode/Coming Soon page option. It is under Appearance > Theme Options > Utilities > Coming Soon. All you have to do is turn on the Enable Coming Soon tab and then choose whether you want your whole site to be redirected to a content-only or full-page template of your choice. You could make any page you wish with the style of your choice and relate it to the coming soon mode.

If you prefer to have the site URL always available when it is in Maintenance (coming soon) mode, you can set it as your home page under Settings > Reading.