But here's some basic information: start here, and here, and here, and read this sticky topic in this forum. If you still need more information, Google "build fiberglass subwoofer enclosure" or something like that. Then, if some part of the undertaking still isn't clear, ask specific questions. There's lots of help available, but you should take the initiative.
Or you could bypass all the research and find a fabricator to do it for you. For that process, read this. Either way will be interesting and educational.
Actually, the most important thing is to have fun getting to the enclosure, not just having it. Enjoy the journey.