I don't believe anyone here on this board has attempted to make one from scratch, but I suppose you could. You don't have to know TOO much about car audio to make a box for a speaker. At minimum, you need to think about if you can make a box you feel will successfully fit in there, and house a speaker. A speaker has a minimum requirement of air space for a sealed box, and some space behind the speaker itself, so you need to take that into consideration, sub depth and volume requirements. With the right volume and some polyfill, you should be okay as long as your box is well made. Those would be the basics.
It's just whether or not what you intend to make and the work spent on it is worth it versus the price of a premade one. The premades vary in price, but some people have gotten some real steals is all... Getting the fiberglass thick enough so the box is solid, doesn't rattle and mounts as tightly as the prefabs would be things to consider.
However, there are some real car audio buffs in here, so I'm sure you would get tons of help if you needed it!
Good luck!
Jon
[Edited by JTang on 07-20-2000 at 11:26 PM]