Polyline with selected points

Hi everyone! I need to draw the lines that appear in red in rhino but can´t figure out how to organize the points in grasshopper. The polyline should be the difference between the bigger rectangle minus the squares in the corners. Any ideas?

utdt_eaeu_tesis2019_modelodesarrollo_centralparktower_paso a paso 10_flor.gh (114.7 KB)

Summed up, I need to make a boolean difference between both surfaces and create a polyline with those points.

You want this ?

Yes, exactly! Could you send me the definition?

utdt_eaeu_tesis2019_modelodesarrollo_centralparktower_paso a paso 10_flor_2.gh (108.7 KB)