Changing a simple coach

[modelsof1900]

Nice!!!!
It looks like you used sheet balsa for the new roof end. If so, think about applying a liberal amount of ACC (superglue,thin) to the wood, and let it soak in. Once it is set thoroughly, you can sand to final finish and paint.
This "hardens" the balsa so it won't get damaged as easily.

At same time when this reply was written I edited my post with a short remarks. I used plywood for the ground structure and I sheeted it by styrene sheets and strips. Thanks for your idea.