This whole explanation is way too long. Just look at the pictures and you will figure it out on your own. It?s not rocket science. If you have any questions about what I did, the written explanation below might be helpful.

The actual materials used aren?t particularly relevant. I think you could use whatever seemed right to you, and get an equal or better result.
Basically you need to figure out three things:
Where exactly do I want the air dam?
How will I attach it to the car?
What materials can I find that meet my requirements for strength, cost, durability, and aesthetics?
Where do I want the air dam?
I wanted the air dam to be close to the front edge of the front bumper for maximum effectiveness. I had originally thought about installing it a little farther back where it wouldn?t be visible, but as I thought about it, I decided I could come up with one closer to the front edge that would work better and would look okay.
How will I attach it to the car?
The Element has six fasteners on the front underside of its front bumper. Four are bolts that hold all the various plastic panels up there together. Two are ?push rivets? or whatever you call those fasteners with the center that you pop up. The push rivets are secured to a couple of metal pieces that underlie the plastics exterior. These six fasteners seemed to be a good way to attach the air dam.
What materials can I find that meet my requirements for strength, cost, durability, and aesthetics?
I don?t have access to any exotic or exciting materials, so I am limited to whatever I can round up on my own. I am painfully frugal, so I wasn?t going to buy any super-cool textured plastic panels or nifty aluminum extrusions. And my finished product had to look good enough to pass my family?s approval. I eventually decided that the landscape edging would be a good flexible exterior covering. I considered aluminum flashing for the exterior, but decided it didn?t have the look I wanted, and would be too hard to shape smoothly. The aluminum binder strip was something I ran across while wandering around Lowe?s looking for suitable materials to build the underpinnings of the dam. Coroplast is a material that I have always thought was cool because it is light, cheap, weather resistant, stiff for its weight, etc, etc. In my internet journeys I ran across people using it to make all sorts of aerodynamic mods to their cars, so I figured it would be a great choice. Gorilla Glue is a product I had heard of but never used. It is a urethane glue that is about the consistency of honey and it cures in about 3 hours, expanding while it cures. It is pretty weird stuff, but it does the job in a way that would be difficult or impossible with other adhesives.