Dream big.

So take an autonomous 3d printer factory into space. a good one... with everything on board your factory capable of mining asteroids, separating the elements, then recombining them into feedstock to use to make, well, anything... including (and this is the hard part) copies of the factory itself. http://en.wikipedia.org/wiki/Self-replicating_machine

So this factory every year does two things. It makes a copy of itself, and it works on making an O'Neill Cylinder. A "Rama" http://en.wikipedia.org/wiki/O%27Neill_cylinder

When it finishes, it starts working on making another.

In twenty years the first O'Neill Colony would be done, and another would be started.

It would receive genetic material from earth, in order to seed this colony with life. A huge variety of plants, animals, insects and bacterial agents, all working together to build a biosphere. Using the same factory to make what it needs as it goes along. doubling in number, gaining efficiencies as the process advances and the technologies mature.

In twenty one years, the second colony shell would be done. the biosphere seeded on this one from earth as well, but some things could come from the first colony, and over time far more genetic variety would be implemented from one colony to another.

Two more shells completed on the twenty second year.

By the twenty fifth year... people from earth start moving in...establishing cities and forming whatever political, social or religious community they desire.

In fifty years, the number of O'Neill colonies would vastly outnumber the number of people currently on Earth. All of them being seeded by the legion of factories supplying plants and animals, and allowing them to propagate.

THIS is what a Dyson Swarm would look like.

Fifty years.
Dream big.
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