Pull values from sublist, add new values to sublist

I am trying to pull out some data from sublists AND IF the data is the same, then I would like the next sublist data to add up. (please see the image below).
The objective is to create one “routine” that permits my office to calculate the total Netto area of a serie of appartmens in a Building Block based on Revit Information and then export it to Excel for further processing.

I just started studying Dynamo a couple a weeks ago, I don’t know if my posted Workflow even make sense/or plausible.

Thank you all in advance for your Inputs.