34. Grab the same vertices then drag the down a little bit in the side viewport :
35. At this step we will model the door. Try to make a nice and easy bended shape and not a straight one.
36. Now I will show you how to make that ventilation hole . I know that the Z4 has the engine in the front but it looks cool. So, first of all we need to close that hole. Select the same edges as me, the use the bridge tool to add a polygon between them :
37. Select the new polygons then add an Inset with the same value (2.0)
38. Delete the polygons then select the entire hole, hold the shift button and drag the contour to the back of the car