Does anyone understand the Pricing Rules?

I have a shop that sells cut vinyl, like for storefronts and office hours. I'm trying to set up a rule where the customer can make their artwork at the size they need, and it calculates the price per square foot. This is something that will be specific for this one product.

I think I need to choose "coverage" for the property, but I am totally lost after that. There aren't any video tutorials and the pricing article isn't very helpful. Is there a resource out there that can help me understand how it works?