Hi,
I'm about to start modelling a version of Chippenham with a branch to Calne. I choose that location as my parents were born in Calne and used the line so it was a natural choice for me but does give me what I want which is a mixture of mainline trains and expresses plus lots of shunting. The advice about the RH Clarke books is excellent, my volume is well used. The other books that might be useful are a number by a local Bristol author Colin Maggs, all available on a well known on line store.
Jon