not really sure on how to make the ENTIRE subwoofer from scratch, but it would be alot better if you have 2 speakers, then make a box out of styrene, then cut the holes in the box to fit the speakers, prime and paint and you should be set
HTH
PS, find a small piece of clear styrene and put it on an angle on one side of the box, and have the speakers wired up, itll look real REALISTIC