Adding thickness to a model

I’m sorry if this has been discussed here before, but I couldn’t find any help after searching.

I’m currently creating a model of a car. I have found that I can model best, for the most part, by extruding the edges of a plane. I’d like to turn the plane into the thickness of sheet metal, but I don’t really know a good method to go about doing this. Has anyone had any experience modeling this way? Or would this be easier to achieve by modeling with a cube rather than a plane? Any and all advice would help. Thanks!

try the solidify selection script
in edit mode
mesh > scripts > solidify selection

there is a great video tutorial somewhere online but playing around with it should be too hard to figure out

That was exactly what I was looking for. Worked on the first try. Thank you very much.