Hello Michele,
I've moved your post to the Schedules forum where it belongs.
I wish I could tell you that what you want is easy or at least 'user friendly', but it is a little awkward using the older "List" scheme mechanism of ArchiCAD.
The interactive schedules are only capable of producing a single line of information for any one element in your model. So, you can get one line listing your floor area, but are not able to get multiple lines/results for the percentages of each tile.
The List Schemes, however, can calculate anything, but are not very "friendly".
We associate what is called a Property Object with your floor slab and tell the property object to compute a quantity of tiles according to your formula as a percentage of the total floor area. I'll show you the steps, but it will take several posts as I can only post one screenshot per post....
I'm working with the US library in feet/inches - vs your metric - but the differences should be obvious...
Step 1: create a new property object: File > Libraries and Objects > New Object
Change the subtype of the new object to Properties as shown here.
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