Page manager, Panels and theme suggestions
If you don't already have one create a yourtheme.layouts.yml file in your theme folder. There you will define the regions, preview icons, and labels.

custom_2col_brick:
  label: Two Column Brick
  category: My Custom Layouts
  template: layouts/custom_2col_brick
  icon: layouts/custom_2col_brick.png
  regions:
    left:
      label: Left
    right:
      label: Right
    footer:
      label: Footer
custom_1col_landing:
  label: One Column Landing
  category: My Custom Layouts
  template: layouts/custom_1col_landing
  icon: layouts/custom_1col_landing.png
  regions:
    main:
      label: Main Region
    footer:
      label: Footer


Now you can create your page__custom_2col_brick.html.twig and page__custom_1col_landing.html.twig files in your layouts folder. Inside there you can define your template. For example custom_1col_landing.html.twig could contain

&lt;div class="one-column-layout"&gt;
    &lt;div class="row main"&gt;
        {{ content.main }}
    &lt;/div&gt;
    &lt;div class="row expanded one-column-footer"&gt;
        {{ content.footer }}
    &lt;/div&gt;
&lt;/div&gt;


Once finished you should have the following files. (The preview icons are optional)

/yourtheme/yourtheme.layouts.yml
/yourtheme/layouts/custom_2col_brick.html.twig
/yourtheme/layouts/custom_1col_landing.twig