For those of you who are having difficulty with the dragon in spite of the guides, as neither of them truly detail the battle, I may have a strategy.
As a result of playing the battle for an hour and a half, the dragon's moveset and mannerisms gradually became clearer.
Ground: Fire- the dragon rears up on its haunches and breathes fire, then lowers its head again
Snap- Lashes out with its head and snaps its jaws at close range
Short lunge- exactly as you would assume, the dragon launches its head across a quarter of the field
Long lunge- the dragon launches its head across half the field, if you are at the opposite edge and cannot walk further it will not hit you
Rear- the dragon rears on its haunches and slams down, this is easily confusable with fire and can knock you down and allow the dragon to quick swipe kill you (watch its neck to discern between the two)
Tail- the dragon lashes out with its tail whip from below, keep up quen and keep rolling, however rely on quen as it is difficult to avoid
Snap from below- after the dragon disappears, this is its other attack, observe all sides and use quen
Fire- the dragon files in a circle spraying fire, quen makes you invulnerable and with a dark set, you should have high incineration resistance anyway
Swoop- the dragon dives at you, easily avoidable with a roll
Now that the moveset is adressed, aside from knowing to roll and abuse quen against the air and attacks from below as you cannot damage it, my advice for you is singular; when the dragon is on the tower REMAIN CLOSE TO ITS FACE.
Simple as it sounds, this was my method for victory, which I managed only with Blasphemers armor and a red meteorite silver sword.
As you roll toward the face and away, the dragon will cycle between lunge and fire attacks and remains focused on these, which keeps it away from its repertoire of attacks from below. These are most liable to kill you. Roll toward it, swing a heavy strike and roll away. After it lunges do the same AFTER its head retracts. When it breathes fire, stand under the flame with quen, you will be invulnerable, and wait for the head to lower. Heavy strike and roll away. If you can manage two heavy strikes after the flame, it SHOULD cycle back to flame and you can abuse this for a bit.
NEVER attack the head from either side, only directly, otherwise it tends to knock you over and then attack you like a bitch when you are down. This kills you.
Again, stay in its general ground attack range, and you should limit its attacks from below and the aerial one (which simply tends to drag the fight out.) If you are supremely cautious, roll toward and away until it cycles to ground flame again and again, and only attack it then. (Remember the two hit loop.) Also, equip two whetstones to expedite the encounter.
This attack pattern is not set in stone, however after trying for so long, and tearing a piece of my skin off in a rage, the proximity rolls seemed to keep it grounded 9/10 times and should allow you to win, no matter the weapon. Patience is key, do not become overzealous with strikes when you might be about to win or you will die...in one hit.