Lol relax! This is my basement shop. The walls don't need to be pretty.

As for the granite... That's the most important thing in my shop. It's called a surface plate, and it's flat. Very, very flat. The difference between the highest and lowest points, over the entire 12"x18" surface, is less than 0.0002".

A surface plate is the reference for the entire shop. Using various instruments, I can use the plate to tell if a part I made is flat, if opposite faces are parallel, or if perpendicular faces are, in fact, perfectly square. I can measure the height of objects relative to one another. I can use it to make other things flat, and then use those things to check the flatness of other things, such as the sliding surfaces between different moving parts of a machine.

Mine is a relatively small surface plate. They can get downright huge. 10, 20 feet long, and 1-2 feet thick. And bigger.