Sounds just like my DS.

My DS rolled maybe 4 or 5 times in total from when he started to roll to when he crawled (11 months). And I can't remember exactly when he did it the first time but I think it was in the 5th month. He just was never much of a roller.

As for sitting on his own, there was no way he was doing that at 5 months. I think maybe around 7 months...but I think the idea is that they are supposed to be strong enough to get themselves into and out of the sitting position, rather than being placed in it...but I certainly put him in the sitting position because it was handy to keep him in the one place LOL (once he could do it, that is). He was commando crawling at 6 months or so and was so quick!

BUT he was always brilliant at standing up, from when he was tiny. He was cruising around the furniture before he could crawl and certainly holding himself up against the coffee table playing with toys before he could get in and out of the sitting position by himself (which I think was around 9 months).

I was really worried about the rolling thing too and I read that babies who are reluctant to roll could benefit from osteopathic treatment so I took him off to an osteo (at about 5 and a half months) who specialised in babies and found that DS actually had some physical discomfort and tension from his birth (forceps delivery) which was discouraging him from rolling but ironically was also the reason he was so good at standing (and holding his head up as a newborn) - he was more comfy upright. He also has a scoliosis in his neck from the delivery which needs monitoring through childhood, nothing major, maybe once or twice a year to see the osteo, just to make sure everything is staying loose and moving freely.

Even with the osteopathy he never became a roller and he walked at 14 months so all was good with his gross motor skills.

Soooo...sorry for long post but I would suggest taking him to an osteo or paediatric chiro first for a check up, especially if you had a long labour and/or very fast delivery.