I have measurements, how do I get them into Layout?

I’m new and I thought Layout would be an easy and fun way to input the dimensions of my side garden and figure out where I wanted vegetable gardens and walkways. I can’t find anywhere in Layout that let’s me decide how big my area is.

All the tutorials I find keep drawing random sided houses and rectangles. I want to draw something I have specific measured out dimensions for. If I wanted to do all this complicated dimensions/ratios of squares I’d just use graph paper. I know if photoshop there is an option where you can change the canvas size to a specific measurement. Is there anything like this in layout?

Draw in SketchUp at the desired dimensions. Send to LayOut to place text and other content.