This is a simple method for calculating gross floor area of a project, using the element schedule feature of AC10. It also gives us an introduction to basic element schedule technique.
The method assumes a tolerance for approximation; you need something to say when they ask, how big is it. If you need precision, you can figure it out I'm sure.
This schedule is provided in the templates, and it can be imported from 3 Resources/AC/Element Schedules. Or you could build it from scratch quite easily.