These are quite frightening modeling wise as they have a stack of horizontal and vertical bits that all have to line up or it looks silly. Fortunately now that I can get evergreen styrene online its a bit easier.
I started with a sheet of N scale siding (0.5mm thick), and cut a piece to size off the plan (13mm deep by whatever long) taking into account that the ends were going to be full width and the sides slightly shorter when it was all assembled. I then lined up my piece of plasticard and used a pencil (one of those tech drawing thingie one) and marked out where the windows were. A pencil line was then drawn across the whole sheet where the bottom of the window was to be, and the lines extended from the top to the line. Cutting the waste away started with cutting the bottoms of the windows (not all the way through) and then using the pre-scribed lines to guide the vertical cuts (which were right through). The waste bits were then removed by snapping them out of the frame. (the picture shows my first attemp in which I screwed up one of the window widths and had to do it all again).
The second layer was made from 0.5mm plain plasticard. Again this was 13mm deep and the same length as the top piece. I marked on the sheet where the bottom of the windows were (the glass bit) and then scribed this all the way across without cutting right through. The 2 pieces of plastic were then laminated together and left to dry. I then marked out the edges of the windows with a pencil and cut them out, cutting the verticals and then snapping the waste pieces out. Any of these lines that were not square got a bit of filing and knife work to tidy them up. I also discovered that one of my files was the correct width to clean the window frames up which made the job a wee bit easier. The bottom beading on the window frames was made by gluing a pieces of evergreen microstrip across at the right height and then removing the bits between windows. Its not ideal but they do all line up which is a bit more important (I'll have to paint it now to check it doesn't look silly and the blemishes are not too deep).
Finally I tacked the bits above the windows. This was cut in one piece from a piece of 1mm plasticard. I was not sure how I was going to do all the raised beading on the edges, and it was a pleasant surprise to discover that the burrs raised from cutting the plastic sheet were just about right. The beading running down the center of this bit was done again using microstrip.
So, here's how it looks after a night being left to dry (pressed under a piece of glass so that it would not warp)
'Don't look too close'