Let me help you along. This code does not check stroke color and also not if the path is visible (not covered by another path). I think both of these things are unneeded, since you will need to flatten the document anyway for printing.

It now returns the color and the square point area.. you can figure out how to convert to square cm..

// get all visible path items in the document
var items = document.getItems({
	type: Path,
	hidden: false
});

for(var i = 0; i < items.length; i++) {
	var item = items[i];
	if(item && item.fillColor) {
		var rect = item.bounds.clone();
		for(var j = 0; j < items.length; j++) {
			if(i != j) {
				var checkItem = items[j];
				if(checkItem && checkItem.fillColor == item.fillColor) {
					// add its bounds to the rect
					rect = rect.unite(checkItem.bounds);
					// nullify, so we don't check it again later
					items[j] = null;
				}
			}
		}

		print(item.fillColor, rect.width * rect.height + ' square pt');

		var path = new Path.Rectangle(rect);
		path.strokeColor = item.fillColor;
		path.fillColor = null;
	}
}