On another note is it the builder's responsibility to clean the windows of cement and crap?
If so I will tell the custy to phone them and get them back.
technically yes, but if they have got someone else in to do it (you), then you charge for it.
your time, chemicals used etc.. all adds up.
if they dont want to pay - then yes, tell them call the builders back as they put it on there - its not your problem as you didn;t do it.