It’s normal for them to start rolling, whichever direction it may be. But what’s important is that there are no hazards around baby that could potentially suffocate him. For me, my baby sleeps in her own cot, which is completely bare, so that even when she’s on her tummy, things don’t press against her nose. This was especially important when she was younger and did not have the full arm strength to push herself up. I monitored her very closely to make sure she was always breathing well. I also didn’t co-sleep on the same bed to protect her.
It’s normal. So don’t worry. Yes, there’s this danger of him rolling when you are asleep. You will need to keep his bed free of clutter, unswaddle him and check on him from time to time at night