The way I did it, I sent up a habitation module first with the cubic docking ports on both ends, then I took each fuel tank up separately. I used very similar launch vehicles to get everything up into orbit. Everything is jettisoned getting into orbit except the bottom-center tank and engine which is used to park the body of the station. The center fuel tank is not used in ascent, it is docked to the station for refueling craft in space. Once in orbit, I undocked the big tank from the command module, flipped around and docked back up with it so that my maneuvering controls would be pointing in the right direction. In other words, the refueling tank rides into space on the bottom of the command module and then is moved to the top once in orbit. There is a T45 rocket motor between the two fuel tanks in the center section that is accessed by jettisoning the lower docking port after moving the refueling tank to the top of the command module. A work in progress, but it already functions as an orbital refueling station.