I want to watch it but Roland is definitely not black. I love Idris Elba but there is no way to follow the movie up with O'Detta being black and having distain early in the series.
Make sure you have a lot of time first. If you go the Audible route Muller does an outstanding job "telling" the story. It is quite the journey if you decide to strap in! Well worth it.
I just finished the series. That was pretty intense. Stephen King really did a great job. His life's work really. It was cool how a ton of his books have tied into the DT series.