Is it best to either of the 2 enclosures that jl audio make for the 12w7 or would it be better the build a custom box for this sub? If you would recommend getting a premade box which would it be?
A sheet of 3/4" MDF ranges from 25-35 in most places, then go to shops and ask for prices for carpet (or whatever you plan to cover the box with). Then you'll have to add the price of wood glue and caulk (not too expensive) and coarse thread screws, unless you have some laying around the house. Shouldn't be too bad, no more than $75, usually 50-60 bucks.
my friends says that he nows how to build them. He also said that he could make a fiberglass one. What goes into making a fiberglass one and how much would it prob cost to make a good one?
You'll need chop mat, polyester or epoxy resin, Hardener, a roller, masking tape, 3:1 pumps, plastic tubs to mix in, acetone, mold release, bristle brushes, and tongue depressors(to mix with). Pretty extensive list, just go to a hardware store and get estimates as prices are different for the stuff.