As regular Trolls, but with the following changes:
Larger: Increase HD to 8d8+48 and Hit Points to 84.
Stronger: Increase Strength by +2 (Str 25).
Smarter: Increase Intelligence to 8.
Horns: Gore Attack 4d6+10 (similar to a minotaur's gore attack).
Weapons and Armour: Common Weapons: Great Club, Great Axe or Greatsword (wielded with one hand or two) plus thick Hide Armour: Increase AC to 21.
Feats: Remove the Alertness feat and add Two-Weapon Fighting or Multi-Attack.
Notes: Some even carry water on them for putting out flames. They are often the leaders of parties of lesser trolls.
Alternatively, treat the Uber-Troll like a regular troll, but with 1 level of Barbarian and with Minotaur horns. The CR is still a 7.