The Clan with the most territory in the homeworlds during the golden century.
Seriously, if you are looking for "Clan builder" that's where you need to look. More territory, more planets, more enclaves, means you need more bulldozers, more construction cranes, more building crews. I'm talking about any kind of construction, from houses to spaceports to trains and roads to military infrastructure.
I suspect there was a building boom all around in the homeworlds during the Golden Century. So which Clan built the most would hinge on a combination of territory size and economic resources.
To my mind, the Wolves, Ghost Bears, Coyotes and Jade Falcons are all reasonable contenders. Remember the Coyotes were once among the largest and most powerful Clans. The Foxes/Sharks aren't in there simply because I don't think they had as much territory as other Clans, but their economic engine was second to none in Clan space, so I have no doubt that they were good builders in the territory they did possess. They also developed things like the Chatterweb and I suspect were a major driver of the entertainment industries in Clan space.