Hi my 5 months old LO can sit unaided but can't roll, he turns to the side like he's going to but never quite gets over and then gives up.
If he's on mine or DH's stomach for tummy time he will roll, but I think that's more to get off as he doesn't like it and seems to get a sore neck and just lies his head down.
He also wants to stand quite alot so is always pushing himself to do new things but is it strange that he can't roll but can sit?