I gotta reiterate this point... PRACTICE LIKE YOUR LIFE DEPENDS ON IT!!!! I dont know one person whose first project came out like they wanted. In fact, I threw out my first few tries untill I got the right technique. If you want some fiberglass help, go to Sounddomain.com , there are a ton of people on there who would be willing to give you some pointers.
other than that, for your box, it really has all been explained fairly well. You are gonna need a gallon of resin or more, a ton of cheap plastic throw-away brushes, a bunch of glass matt and cloth.... its an expensive project !!
as an example, 2 months ago, before my system was stolen from my 92 Caprice, I finished a 2 week project of building a COMPLETELY fiberglass box housing 2 15" Adire Tempests. Total project time 12 days (on and off between work and whatever else), total cost - $230 for supplies, when finished I used 4.5 gallons of resin, 26 paint brushes, 10 packs each fiberglass mat and cloth, one can of bondo lightweight filler, 1.5 sq. yards of heavy fleece, a 2x4 for bracing and 2 cans of rubberized undercoating to dampen the inside of the box. The box is approx. 7 cu. ft after bracing and displacement.. its a HUGE piece of fiberglass
(in fact, its for sale right now because all of my amps were stolen, and I got the Bonneville, so I dont need the box anymore...
damnit...) then again, you probably dont need to make the whole thing fiberglass so your costs wont be nearly as much, as you will be able to fab a base out of wood (Medim Density Fiberboard) instead of fabing it out of fiberglass.
But if you take your time, be patient, and be CAREFUL to not spill the mixed resin on yourself (it BURNS!!!!) you will have a great looking and great sounding speaker box! Practice up and have FUN!