When Shepard exits the elevator some Geth will be attacking. Kill them. Then get in the Mako. Just follow the skyway. As Shepard leaves the garage Geth Armatures are dropped off. Kill them. Then continue down the skyway.
There will be more Geth at the top of the incline. After they're dealt with continue on into the Weigh Station. When the road bends to the left will be a ramp down that Shepard can only go down on foot.
Talk to Juliana and ask about the Headquaters. She'll also ask if Shepard can look for her daughter who was last seen in the headquaters.
After the conversations head back to the Mako and time to climb some ramps. When Shepard reaches the top the road goes left. When the door opens there is a Geth greeting party. Greet them weapons blazing.
Follow the road and about halfway down is more Geth. Greet them as well. At the end will be the ExoGeni Headquaters. Shepard can't go any farther in the Mako. Bail out of the Mako.
Fight the Geth and to the left is the entrance to the ExoGeni building. The entrance is blocked with a force field. In front of the door is a trench.