I agree with building it yourself if you plan to experiment. If you're looking for a quality build, I'd **** it up and buy one from a professional car audio store. Give them the model of your speaker and sound preferences. They'll build a box to match it, and they'll most likely guarantee it. If you don't like it, take it back and try again.
So, if you're just looking to experiment go ahead and build it yourself, but if you're looking for quality, buy one.
Hope it helps.