I was just yesterday describing in detail how I create BOM:
It refers to example files I gave some time ago:
As I do it with spreadsheet there should be no problem to add to each footprint area it occupies and get sum of all elements areas. The only problem to be solved is probably that in my spreadsheet number of elements I probably treat as text and not number.
You can assume typical % occupied by footprints to count expected PCB size.