WARNING: I feel that, although this tutorial is seemingly safe, I must caution everyone to build this at your own risk. After all you are dealing with a hot glue gun so be sure to take safety measures to protect yourself and property. Do this at your own risk!
Now that I'm done covering my butt; here is a brilliant tutorial on how to build a hot glue web gun. The genius thing about this gun is that it eliminates the need for a air compressor and instead uses a air inflator commonly found with air mattresses and swimming pools. Check it out: