My father was a HO nut in the 50/60/70's and did this to escape from mother, I remember him well building each individual building 1 piece of wood at a time as if it were real (that was the Mechainical Engr. in him)
As such I pose this one question to you - If the paper product is as good as they appear to be, and they do look great, why spend the time on an endever that cannot be improved upon? My years in engineering with the Japanese taught me this to the core, never use wood when cardboard will do and never use cardboard when paper will do.
Good luck, why not make some frames for simulated mountains and rivers that he can cover with lath and plaster.