I filled in 1/2 of one of the kitchen windows with plasticard.The ends i thought I would be clever and just get some spare Hornby LMS flat ends, good plan except the curved profile for the roof is totally out.
So I glued the ends on and the filled the rest up to the roof line.
When dry, I carefully sanded to shape and painted the roof.
I believe the width my be slightly out but who has their micrometer handy when they are trundling round a layout ?
If you want to get really critical the door windows on (all) the Colletts are the wrong size and shape as well.