Thank you Xpertskir for your answer, it is very helpful - I have to say I thought it is to easy a solution. I have access to a spectrophotometer to measure the lovibond so your advice to roast my own sounds fun and with the right equipment it could be an accurate solution, would you agree?
I don't have a specific recipe in mind, as I mentioned I am just reviewing what is possible to brew in Brewing classic styles. My ultimate goal is craft brewing, but I believe that I should first master brewing the "classic" styles. That is is why I what to be as accurate as possible to the recipes, because I know close to nothing about various ingredients' contributions to flavor and that is what I want to learn.
I think this forum might be very helpful!