You could, if you're going for orbital stuff rather than PDC's stick a single Orbital Habitat Module on, that's only an extra 250 Ktons and it allows you to use your construction factories to make it. Generally when I'm using orbitals to terraform rather than population run ground based stuff I make each one the equivalent to 10 ground based terraformers, you're then looking at around 250 Ktons just for the terraforming modules anyway and at that weight doubling it doesn't really increase the cost that much.
For example:
X-T01 class Terraforming Base 565,400 tons 1540 Crew 8174 BP TCS 11308 TH 6000 EM 0
530 km/s Armour 1-609 Shields 0-0 Sensors 1/1/0/0 Damage Control Rating 1 PPV 0
MSP 9 Max Repair 500 MSP
Intended Deployment Time: 3 months Spare Berths 2
Habitation Capacity 50,000
Terraformer: 10 module(s) producing 0.02 atm per annum
Prototype Admiralty 2500t M50 Ion Drive (20) Power 300 Fuel Use 4.42% Signature 300 Exp 5%
Fuel Capacity 10,000,000 Litres Range 71.9 billion km (1571 days at full power)
This design is classed as a Commercial Vessel for maintenance purposes
This design is classed as an Orbital Habitat for construction purposes
Is a self propelled Orbital that can be built using industry and is only 2000BP more than the same amount of Terraforming Installations, adding a tractor beam would, I think, allow you to daisy chain several different Orbitals together (weapons platforms, terraformers, habitation modules, etc.)
X-T02 class Terraformer 314,350 tons 1510 Crew 8068 BP TCS 6287 TH 6000 EM 0
954 km/s Armour 1-411 Shields 0-0 Sensors 1/1/0/0 Damage Control Rating 1 PPV 0
MSP 16 Max Repair 500 MSP
Intended Deployment Time: 3 months Spare Berths 1
Terraformer: 10 module(s) producing 0.02 atm per annum
Prototype Admiralty 2500t M50 Ion Drive (20) Power 300 Fuel Use 4.42% Signature 300 Exp 5%
Fuel Capacity 10,000,000 Litres Range 129.5 billion km (1571 days at full power)
This design is classed as a Commercial Vessel for maintenance purposes
While this design has to have a dedicated shipyard and is and is only 100BP cheaper than the Orbital Habitat version.
To be honest a lot of it will be down to your own personal choice, but I think we can all agree that prefabbed PDC's suck unless you've already got the IC in place to assemble them, and in that case you can build stuff directly on that body anyway. Perhaps Steve could increase the effectiveness of Construction Brigades, but increase the cost in order to keep them relatively balanced?