For some reason I seem to be one of those people who will always try something the hard way first and then about half way through realise that there is a much easier option.
So far I have made 8 buildings -mostly terraced houses- for my 6mm campaign which involved a lot of windows all painted by hand. I was in town today when the light bulb flashed on; instead of painting them why not use a chisel-pointed permanent black marker pen. So I've bought one and will try it out...I have high hopes.
I know, sometimes I even amaze myself.