Alright then, I don't mind dropping the Training Rules.
Since this leaves the Common Roc pretty well done as it is, shall we move on to the Great Roc?
We can get most of the way there by upsizing the Common Roc to a 24 Hit Dice Colossal Magical Beast, increasing its Intelligence to Int 6 and having it speak Common and Auran.
It gets an extra 6 skill points and 2 feats from its higher Hit Dice. The skill points should probably be equally divided between Listen and Spot, but what do you fancy for the feats? It's got enough HD to be eligible for Epic Feats, so I'm tempted by Epic Will (to give it a +16 Will save) plus Hover (so it can make mid-air full attacks while blasting opponents with its downdraft).
The Great Roc's a slower flier (30" vs 24") so I'd drop its speed to fly 60 ft.
It also has a 2 point better AC, so I'd better up the NA up a bit - I think I'll aim for AC 20, for the sake of argument.
Apart from that, I'm thinking it could deserve an increase to its Wisdom and Charisma (maybe +2 apiece for Wis 15, Cha 13?) and it has a couple of special abilities - rock-dropping and communicating with Common Rocs.
Boulder-Dropping - are we making these boulders 3d10 damage like the entry says, or shall we have them do heftier damage? Hmm, a cloud giant throws a Huge rock for 2d8 damage, if we scale it up from that a Great Roc would drop a 6d8 damage boulder and Two-Headed Roc drops 2 4d8 boulders. That seems more appropriate to me.
I'm also wondering whether the Boulder-Dropping damage is doubled in a dive - solely because I like the idea of a dive bombing Colossal Roc!
Communicating with Common Rocs - maybe we could expand this so it can talk to any predatory bird (Giant Eagles, Owls, et cetera)?
Putting it all together, I'm suggesting:
Roc, Zakharan, Great Roc
Colossal Magical Beast
Hit Dice: 24d10+216 (348 hp)
Initiative: +2
Speed: 20 ft. (4 squares), fly 60 ft. (average)
Armor Class: 20 (–8 size, +2 Dex, +16 natural), touch 4, flat-footed 18
Base Attack/Grapple: +24/+58
Attack: Talon +34 melee (4d6+18) or boulder +18 ranged (special)
Full Attack: 2 talons +34 melee (4d6+18) and bite +32 melee (4d8+9) or boulder +18 ranged (special)
Space/Reach: 30 ft./20 ft.
Special Attacks: Boulder-dropping
Special Qualities: low-light vision
Saves: Fort +23, Ref +16, Will +12
Abilities: Str 46, Dex 15, Con 28, Int 6, Wis 15, Cha 13
Skills: Hide -7, Listen +13, Spot +17
Feats: Alertness, Flyby Attack, Hover, Iron Will, Multiattack, Power Attack, Snatch, Wingover plus one more (Epic Will?)
Environment: Warm mountains and island forests
Organization: Solitary or pair
Challenge Rating: 13
Treasure: None
Alignment: Always neutral
Advancement: 25-72 (Colossal)
Level Adjustment: —
A Zakharan great roc has brilliant, multicoloured plumage. Their wings and backs are typically a shade of green or gold and their beaks range from pale ivory to a rich shade of brass. The leading edge of their wings is a glorious azure blue. Male great rocs have crests of the same bright blue hue, while females have snowy white breasts. The egg of a great roc is the colour of ivory, dappled with beautiful patterns of turquoise and indigo.
These enormous creatures are 120 feet long from their beak to the tip of their 40-foot long tail feathers, with wingspans as wide as 270 feet. A typical Zakharan great roc weighs between 200,000 and 250,000 pounds.
Zakharan great rocs speak Auran and Common and can speak with any avian creature (as if using a speak with animals spell).
Combat
A roc attacks from the air, swooping earthward to snatch prey in its powerful talons and carry it off for itself and its young to devour. A solitary roc is typically hunting and will attack any Medium or larger creature that appears edible. A mated pair of rocs attack in concert, fighting to the death to defend their nests or hatchlings.
Zakharan great rocs like to crack tough opponents, ships or fortifications by dropping boulders from the sky.
Boulder-Dropping (Ex): ?
Skills
Rocs have a +4 racial bonus on Spot checks.