Build Dai-Oh (ビルドダイオー) is an auxiliary mecha from Ressha Sentai ToQger, the 38th Super Sentai series (2014–2015). It is the personal fighting robot of ToQ 6gou, the team's sixth ranger (orange), and represents the "Warrior Mode" of the Build Ressha (Build Train). ToQger was never adapted into Power Rangers, so Build Dai-Oh remained exclusive to Japan and was never released as a Power Rangers toy by Bandai America or Hasbro. Unlike the series' main Megazord, ToQ-Oh, it is a support-class mecha on the same tier as Diesel-Oh.

On screen it forms from the double-decker Build Ressha, whose two cars can stack on top of one another. To transform, the rear cars fold down into legs while the front cars become the arms, and a small crane forms its head. Its defining trait is modular, swappable weaponry: the arms can be exchanged for other Ressha, such as the Drill Ressha (Crane-Drill finisher), Tank Ressha (heavy punching attack) or Shield Ressha (forearm shield). It can also join ToQ-Oh and Diesel-Oh to form the larger combination Cho Cho ToQ-Dai-Oh.

The DX toy was produced by Bandai (Japan) as entry No. 11 in the "Ressha Gattai Series," released in mid-July 2014 at ¥6,500. It is made primarily of plastic (ABS/PVC), with the train measuring roughly 32.8 × 22.2 × 7.2 cm and weighing about 800 g. Transformation is deliberately simple — fold the limbs out and rotate the head. The key play feature is full compatibility with the wider Ressha gimmick system: the arms detach and can be replaced by any other arm-type Ressha, and Build Dai-Oh's own arms in turn attach to ToQ-Oh and Diesel-Oh. No US or Power Rangers version of this mecha was ever made.