4L layout with an extra row under it

Hi there!

I’ve been trying to understand the workings of the layout system to create my own custom layout.
I’m trying to make a 4L layout with an extra full width row under it (4L meets 4F kind of thing).

Is there any info on how to construct a custom layout?

You may only use the predefined patterns:
In your case you may try to create a 2E layout and place the 4L layout in its first cell: