Coming soon page can be created with Blank page template and Visual Composer modules. Create a new page in Pages>Add new section, enter title for it and select Blank page template in Page Attributes section.
After that begin adding page elements. You can create any layout for Coming Soon page with Visual Composer modules.

You can also add a background in Row settings. More about background variations you can read in Row background variations article.

There are 4 Coming Soon styles represented in Polo demo. Click on the links below to view them:
Coming Soon with simple background image
Coming soon with background image and dotted overlay