When I tried to have some Unit mix ratios in the Revit Schedule. It was challenging to have it work
I figured them out finally and shared how to do it for my record
Add Quantity (Shared parameter)
The parameter name can be anything, It doesn’t have to be “Quantity” The Revit Count parameter can’t be used in the formula, so you need something to calculate with
Count% (calculated parameter) Quantity by unit type
Unit mix (calculated parameter) Quantity % by grand total
Ave Area Area * Count% / Quantity