Here is another picture from the out takes video showing the Euston end of the NE wall.
I have these two books which you may have come across.
The first image from the Midland Main Lines book shows the flat roof being installed in 1934.
The caption text 42 & 43 refer to the next images which show some detail of
The NE wall at the turntable end.
The final image from the Euston book is from 1964, with the roof having been removed and showing the internal aspect of the NE wall