How to create a masonry layout

Hi there...

I'm trying to create a simple masonry grid with images as backgrounds and one line of text over the image.

I used PostX Pro but can't seem to get it to order the display of boxes the way the client wants to order them.

https://drive.google.com/file/d/1NXczLIYHKqvrQ8kUgVDJm8fu7RIGzYFu/view?usp=sharing That's a screenshot of what I'm trying to do.

I'm using GenerateBlocks Pro, so if that's where I need to go, let me know.