Summarize this article in one sentence.
Lay the next door panel on the workbench. You'll install the hinges the same way you did before, only this time you'll leave the trackless side empty. Align a hinge in 1 of the corners and in the center of the panel, then screw them in place. Leaving 1 side bare makes fitting and installing the track easier, so do this for every panel. With a friend, pick up the new door panel. Fit it on top of the first one, taking care to line up the side edges. Move the hinges on the first panel so their tops are on the second panel. See how they align so you know where the screws will go. Pre-drill pilot holes there, then fasten the hinges in place with more lag screws. First, place the roller in the hinge. Place it over the empty corner of the door panel, but don't fasten it yet. Bring the remaining roller track over and fit it around the wheels, then screw the hinge in place. Line up the remaining track so it's against the door frame. Slip screws into the brackets to secure the track directly to the door frame. Before moving on, tighten up the screws in both track brackets as needed. Remember to leave a little bit of space between the track and door frame. Set up a couple of ladders on 1 side of the door. You'll need someone to help you lift the track and hold it in place. Line up the curved section of the track with the track piece you placed earlier. Slide screws into the track holes and ratchet them in place. You'll need a pair of 114in (3.2cm) angle irons from the home improvement or hardware store. These need to be screwed to joists in the ceiling. Near the end of the tracks, connect the angle irons and tracks with a pair of supporting brackets. To find the joists, use a stud finder. Purchase a pair of 112in 14in (3.81cm 0.64cm) stop bolts. These go at the end of the upper tracks. Slide them into the holes, facing the threads towards the inside of the track. Then fasten them with a ratchet wrench. Continue stacking and securing the panels together with hinges and screws. When you reach the last panel, don't install the hinges or wheels yet. Be careful, since the panel will fall forward if no one's holding it in place. The hinges on the top panel need to be placed partway down the door. Line it up so the wheels rest on the curved part of the track. Finish by fastening the hinges in place with screws.

Summary:
Install 2 hinges on the next door panel. Place the second panel on top of the first one. Use the hinges to connect the door panels. Install the remaining hinge and roller. Fasten the track to the wall. Connect the horizontal track pieces to the vertical ones. Fasten the tracks to perforated angle irons. Complete the tracks with stop bolts. Set the other door panels in place. Secure the top hinges and rollers to the curved track.