Create openings in a surface (facade) according to a ratio


I want to do something simple : I have a bunch of facades that represent individual units. I need each unit facade to have a Window-Wall-Ratio of 40%. I could go in and draw windows on each unit to 40%, but this will take forever since most units are different. Can someone help me make a script? I need two windows in each unit, that are offset from the center like so :

Each window should be 2m high, start 0.3 m above the floor.

Can someone help with this? thanks.