I bought
Paul Kirk's Championship Barbeque Sauces from Amazon in 1998 (!). The book walks you through making your own sauces and rubs with worksheets and ratios. It is really a great book.
Traditional BBQ sauce is comprised of tomato, an acid, and a sweetener. I went to the grocery and bought a whole bunch of store-bought sauces. I tasted them all one at a time and read the ingredients. I discovered that the ones with the sweetener listed first were my least favorites.
I used Kirk's book and started experimenting. He also talks about "flavor prints". I wanted a Louisiana flavor print. After a dozen of so small trials, I settled in on a style I liked.
Mine is base is Cider/Cane Vinegar, Tomato, and Cane Syrup/Brown Sugar (in that order). Then I used Louisiana-centric flavors: Cayenne, Garlic, Onion, Allspice, and Clove. (Allspice and Clove are key ingredients in Louisiana seafood boil. I use them very judiciously in my sauce as they can be over powering.
I also discovered that my sauce is much improved with just a tiny bit of liquid smoke (pecan) or dark coffee.
Once I got my recipe right, I started making it 40 quarts at a time and canning it in mason jars. I have a fairly large number of friends that expect bottles periodically.