If you're looking to do an elaborate a page builder with ProcessWire and don't want to pull your hair out, I highly recommended viewing this video:
A couple notes:
with the css grid specification, you can assign multiple blocks to the same grid-area but they will overlap each other. I've "overcome" this by combining multiple blocks into a parent div and assigning that instead. pretty easy to do.
i didn't demonstrate it, if your blocks have a grid structure within the