To give the hood a more rounded shape at the top go into Edge sub object mode and select the edges that go around the top of the object as shown in the fig.06, then use Chamfer to taper it as shown in the other picture fig.07.
fig.06
fig.07
Mirror the hood over and adjust it so it fits the short hood then attach the two objects together. (fig.08)
fig.08
Lets start on the cab, start off by dragging a box out in the front view that matches up with the cab as close as you can get it then adjust the Width Segs to 6, once that is done convert the new box to an editable mesh, go into vertex sub object mode and adjust the box so it fits the cab. (fig.09)
