You are on the right track, so to speak. However it is doubtful if you will get the compound curves required for the roof ends by heating styrene. Hence my posting asking about vacuum forming.
I am in the middle of the only book I could find on VF and will say that it is all very doable at the home hobbyist level. There are also a ton of uTubes showing various homemade setups. I am headed in that direction. I plan on using .06” styrene for the roofs.
John Hall (former Reading S scale decal man) was kind enough to send me a Reading construction drawing of the coach roof. It has all the correct contours for shaping the end. John is a vast source of Reading knowledge. I am still searching for some roof vent details, but they seem to be allusive… I probably should try Bill.
If you are not a member of the Reading Modeler forum ( http://www.readingmodeler.com ) I would recommend joining just to see what and how others are modeling in the Reading format. One fellow, in particular, is a marvel of scratch building Reading engines. He has step by step pictures so you can see hos whole process. His picture site: http://www.flickr.com/photos/60361449@N02 You won’t believe what he does.