Its not as though hes just learnt to roll, hes been doing it ages so why now?
It's just that he's got good at it now. It's a really common and usual phase to go through.
Just to make you feel even worse (sorry!) They usually go through similar phases to this when rocking on all-fours (precurser to crawling) and the hardest to deal with is us when they learn to pull to standing. In fact I'd go so far as to say if you don't crack this before pulling to standing it becomes intimately harder to solve at all.
The key skill you are aiming to teach is: in order to go to sleep you must be still.
Consider the logic in this so that you know you are right in teaching it and don't doubt yourself when teaching your baby. Some very basic needs when going to sleep are to be still, quiet and calm. No one can relax their body enough to go to sleep without first being still, quiet and calm.
Some children go still, quiet and calm naturally when tired. Most babies I know don't do this naturally. They are like spaniel puppies in that way. So I would go through a process of physically teaching baby to be still.
This will involve a lot of hands-on presence from you. Firm hand on chest/back in the cot. Maybe holding child a hands on one of yours over their chest if arms are waving around. Second hand can hold legs still if needed.
The firm hand is not about restraining the baby. It is about encouraging stillness and discouraging movement, but not about fighting against them.
So if the squirming against you gets to feel like baby is fighting against you, lessen where your hands are and see if baby is looking to shuffle and change position. If settling into a new position, put hand back on chest/back/side (depending on position) and continue to encourage stillness and discourage movement by holding still in the cot.
If the squirming which results in you listening your hold on baby and it isn't a shuffle baby is after, it is flapping around and trying to get up etc - this is what you are teaching baby he needs to not do. So i wouod lift baby slightly and lie back down immediately. Like a reset button to show that all this moving is not meant for bedtime. That bedtime mean:
Keep noise to a minimum. Keep your movements to a minimum. Just be reassuring and consistant that baby needs to still. Remember that baby simply cannot go to sleep with this amount of moving, so the stillness lesson you are teaching is necessary and vital. Remembering this will help you stay consistant.
As I said, you'll solve this and it will reappear when rocking on all-fours starts. And again when standing. So this technique may need to be revisited several times.
I should just add that another way to solve this is full body cuddling when cosleeping, ifcthats your thing.
And the same technique is likely to be needed for daytime naps as well as bedtime and any wake ups. But it should be short lived. If you're consistant you can usually solve the stillness thing within a month, often within a couple of weeks.