Rails new --builder

When invoking rails new with the --builder option, I see that you have
to call the class ::AppBuilder. How can you
change the source_root for just a few of the methods?

I want to generate the gemfile from my own template

AppBuilder < Rails::AppBuilder

def gemfile
template ‘Gemfile’
end

end

How can I change the Gemfile template from the AppBuilder and if I
can’t what is the use of the --builder option?

thanks,

Dominic