How do you build and play a Thief Rogue?

Ability scores

Dexterity is the dominant ability because it powers attacks, Armor Class, initiative, Stealth, Sleight of Hand and many thieves' tool checks. Constitution and Wisdom are common secondary choices.

Weapons and Sneak Attack

A finesse or ranged weapon remains the Thief's main combat tool. Fast Hands is valuable because it can handle an object, lock, trap, or Sleight of Hand task with the bonus action while leaving the action free for that Sneak Attack weapon attack.

Action economy

Use the environment. The Thief gains the most when there are doors, traps, locks, elevation, objects, equipment and terrain to exploit. Fast Hands can free the normal action for an attack while the bonus action handles a practical interaction that would normally consume an action.

Skills and Expertise

Stealth, Sleight of Hand, and thieves' tools are the most thematic Expertise choices, but Perception and Investigation can be just as valuable in trap-heavy adventures. The best selection depends on whether the Thief is primarily a burglar, scout, dungeon specialist, or urban infiltrator.

Common mistake

The common mistake is reading Fast Hands as 'activate any item as a bonus action.' It specifically expands Cunning Action into Sleight of Hand, thieves' tools for locks or traps, and the 2014 Use an Object action. Magic items with their own activation timing do not automatically become bonus actions.