When you create a new template in the layout template builder, you start off with a specific default set of rows and regions (3 rows, with each one having a single 100%-width region in it):

It would be useful to present options to copy the regions/rows from existing layouts. Here's a rough mockup of how that could look like:

There may be many such presets to chose from, so they could be hidden in a fieldset instead; or the "Copy regions from existing preset" thing could be a link that opens a dialog.
If #4483 is rejected, then we could add these presets in the "Add template" step (where we ask for the name and description of the template):

Anyway, the purpose of this is to allow people to quickly get to where they need to, by allowing them to select a preset that is closer to the regions they need. They could then tweak it to get to 100%, instead of having to start from scratch.
Recent comments
well @herb I cannot believe it, but the webform module was there in modules on the disc, but missing in the listed modules, so I delete the module folder, and downloaded it again. Then...
My Webform Worksheets have disappeared
The only thing I can think of is to make sure Webform module is enabled and that the content type that needs to contain the webforms has Webform enabled for it. Edit the content type and make...
My Webform Worksheets have disappeared
@yorkshirepudding, In the end I fixed it by deleting the config/active folder contents, copying the config/staging/ files into config/active, importing the database again and clearing the caches...
Importing the staged config throws an error: another field with the same name already exists