Lining up and resizing in Unity?

Hey guys,

So basically I am half way through the roll a ball tutorial and I am on the tutorial 'setting up the playfield' at the bit where you add the walls.

at just past 1:45 on the video, the man tells you what to put for the scale value of the wall in transform so it fits exact against the ground plane.

I am wondering how you would work out what to put as the scale value yourself to easily put up walls around a playfield like in the tutorial.

Thanks in advance guys,
Your friendly neighbourhood spiderman