there was a QA talking about this. If you are late to the party, you will indeed miss out on the foundational creation of buildings. You will be forced to only help maintain it. However, they mentioned that it will involve a tier system. Tier 1, it can be built quickly by very few, possibly even 1 settler, tier 2 requires more and more settlers to contribute to reach an upgrade. Tier 3 will require massive amounts of contribution. This means the final products will not spring up over night, but require consistant work by many settlers. It also seemed that the "upkeep" was simply a way of extending the buildings duration. If this timer drops to zero, it will go away, and you can restart the process of building a new one. This will allow for the degradation and rebuilding of settler buildings over the lifetime of the server.