I have been working on designing a car. Only about 10 percent of the time when I make a shape does it become solid. Mostly they just look as if the are a wire frame. I have made sure that the shapes are closed, even sub-dividing them into smaller shapes in order to make sure the are completely closed. Sometimes it will make the new shape solid but half of the larger shape stays empty and other times it does nothing at all. Any suggestions on how to fix this issue? Thanks in advance.

Attached is the file I am working on if that helps plus a pic of what I am doing.

CarSketch.skp

So i am a teacher and helping a student with a personal project. I am simply a beginner at sketchup and am working way above my skill level. I am trying to help him create a car model and right now I am working about 2 or 3 steps ahead of him in order to guide him along the way.

My Issue:

I created a profiles view of the car based upon a tutorial i found on Trimble. That went fine. Now i have begun to create the actual 3D model of the car, but as i am making panels some of them fill in solid with shading, but most are just empty as if they were a wire frame. I have tried to close it into smaller shapes and zoomed in to make sure that the lines are actually connected and there are no gaps, but these are not helping. It seems random to me when the shapes will fill in and when they won't. Is there any way to manually select a shape(by highlight in blue each line) and fill it in with a command? Or some other way to fix this problem?