Buy a RoboRaptor or RoboReptile or similar.
Get hold of voltages, signals, etc from brain to limbs.
Get hold of physical characteristics of limbs and motors.
Calculate the relevant characteristics for a RoboRaptor made out of steel, 4 meters tall.
Find way to alter timings in RoboRaptor software: stride timings etc.
(Underclock? Reverse engineer and alter?)
Order parts, forge steel limbs, teeth etc.
Add a separate, remote-controlled off-switch.
Turn it on and retire immediately.