What were your stats and what weapon did you use? I've been trying and trying and can't dodge roll through his attacks, I'm constantly getting hit, I tried for a few hours and am not joking when I say the lowest I got his health was 20% down. I try and stay in front but am not good at maintaining it.
I would love to get through him since he's my last non-story boss.
That was the Chaos blade IIRC, dex build so maybe 40-45 dex, roughly around the same for HP probably? I can't remember off hand, but I was probably around level 100 or so with a main focus on dex, HP, and stamina (endurance).
People tell you to "not use the lock-on" but I find the opposite is true. You
will lose the lock-on often as the camera goes bonkers when he's close, and that can be a bit frustrating (my only issue is the arbitrary loss of lock-on that happens randomly when you're too close, e.g. at 0:23 and other places), but do try to center the camera and/or lock-on the head as much as you can.
Fight him like you'd fight Amygdala in the Defiled Chalice dungeon, assuming you played Bloodborne; basically, stay in front at all times but keep a semi-generous distance, bait its attacks, and
let him throw his tantrums; when he's done, he will lower his head, giving you a chance for 2-3 hits, though never really much more than that unless you have a very fast weapon.
The important part is patience and not to get greedy. Let him throw his tantrums, then when he's done, punish the head, then retreat back to a safe distance. The only time you might actually want to rush
in during the attack is when he does the laser-beam follow-up to his flame-breath; in my experience it's safer to close in because the laser beam covers an outward arc and it won't hit you if you close in.
The trickier attack to dodge, IMO, can be the insta-charge when he's far, there's a tell but it's short and you do need to be quick, I sometimes got hit by that even after being practiced with it, but it shouldn't be a OHKO.
Good luck!