Ringworld/Sphere World

[Suicide Junkie]

Ah, but when you are retrofitting, to get around the 50% increase limitation, you must retrofit multiple times.

As soon as you do the second retrofit, you've spent more resources than it would cost to build it directly.

Even if you retrofit from Plating or somesuch directly to Placement, you must pay full price for the Plating, and then a whole bunch more to remove the Plating, and even more to add the Placement generator.

You pay tons of resources to speed-build.