Sleeping issue with my 5 month old LO

Hi mummies, Need some advice here. My little one is going to be 5 months old soon and I wanted to start sleep training for him. Wanted to use Ferber method but I am met with some challenges which I am not sure if most babies are like that or just my LO only. 1. He just learnt to roll over. So whenever we put him down to pat him to sleep, he will roll over. If we stop him from doing it, he will cry out really loud and insists on turning over. Hence step 1 of sleep training failed. Does anyone’s baby like to roll over as long as put onto bed? 2. When baby finally able to fall asleep, we thought it’s ok already and walked out of the room. But minutes later, he will scream and yell on top of his voice suddenly. Ferber’s method said wait before going in to pat him. The problem here is, he is screaming and if wait too long, he will cry until cough and till voice hoarse. No use patting him coz he won’t calm down. We need to pick him up. Though picking him up and rocking him and using soft soothing voice reassuring him, he still scream and cry ?. I do not know why he will scream and yell suddenly even though he is tired and wanting to sleep. Does anyone’s baby having the same problem? How do u calm baby down? Thanks in advance. Need some help to make sure I am sane.