Generation 01, Generation 02 and Generation 04.
Dalek society was strictly hierarchical and caste based. The majority of the Daleks seen by other cultures were from either the Military or Scienctific castes. The Worker caste was genetically engineered to be able to follow specific orders and perform specific activities only. Placed within a "Construction Drone" casing, it was these Daleks who built the race's structures, transports and vehicles of war. In later years, much of the construction was automated according to blueprints or performed by slaves – but all Dalek vessels still maintained a force of worker embryos and casings within their incubation units up until the onset of the Fifth Generation.
Smaller than a standard travel machine, the Construction casing had a series of manipulator arms on a revolving collar that allowed for a variety of functions to be performed. The lower half of the casing was shorter than that on a regular Travel machine, with space for only thirty-nine (39) sensor globes. Because the casing was shortened, it was also narrower at the base, allowing the Construction Casing to access smaller confined spaces than regular Dalek casings. Above the strengthened mid-section, the dome of the casing was the same size as that of the Mark Two and Mark Three Travel Machine and it had the same features as those models – two luminoscity dischargers and a single eye-stalk.
The habitation module was located in the mid-section, behind the strengthened, rotating collar that held the various manipulator arms. The nutrient tank was located above the habitation module within the dome section. Due to the dangerous nature of the work undertaken by the Workers, a number of accidents occurred that resulted in the drowning of the worker drone in the very fluid that was designed to keep it alive. This design flaw was never rectified as the worker caste was considered expendable.
Beneath the habitation module, basic life support systems were located. The Construction Casing's power plant was powerful, allowing enhanced mobility to the unit. The motivator units enabled workers to move far faster than a regular Dalek and they could levitate up to five meters above any surface. Small thrusters enabled the casing to maneuver whilst airborne.
This is a conjectural design based on the need for the early Daleks to have some way of constructing new cities, ships and other technologies.