A rough draft. Comments welcome.

I am not going to expand this to a full class entry, because the likelihood of one of my players taking it is pretty low - if you have Player’s Companion, though, this should be sufficient.

HD: d4; after 9th level, +2 per level.
Prime Requisite: INT.
Saves: Thief.

Build Points: HD 0, Fight 1 (thief), Thief 3 (10 skills).

Armor: Narrow.
Weapons: Restricted (2 customs).
Fighting Styles: Two-Handed Only (1 custom).

XP: HD 0, Fight 500, Thief 700. After 8th level, 100,000 per level.

Thief Skills: Open Locks, Find Traps, Remove Traps. (7 customs).

Custom Powers:
Master Craftsman (3× one Craft proficiency).
Attention to Detail (grants +2 on all proficiency and thief skill throws) (3 customs).
Design, Build, and Repair Automatons (3 customs).
Personal Automaton.

I like it!