Is there a way to cull or branch a list according to layer??

Is there a way to cull or branch a list according to layer??
The definition as a whole takes a file in rhino with "buildings" and wants to calculate the cumulative area of their floor plates and stream that into excel Each building will be in a different layer (which is the first column of the excel file) The second column is the footprint of each building (the area of the first floor) - and the final one (the problematic one) is the cumulative area of each volume (ie the floor plates) the rhino file attached is a very simplified thing to see if the script works but in the real file all the floor plates vary a lot [er level so I cant just take the bottom one and multiply it... all areas are different

please help me!

thanks!

monica

test%20areas_monica.ghx

test%20areas%20monica.3dm