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 them (like built with flexbox), you can still assign that block to a grid-area. so if your blocks themselves have a grid structure, that's ok. for example, if your css grid layout is 6 columns, but you have a block that has a grid inside of it (built with like uikit's grid that's 5 columns), you can assign that block to the grid-area.
with the css grid specification, the flow of the blocks does not have to match the flow of the grid-areas. this is insanely powerful.