for what it's worth, check out the manual for the partsexpress.com BR1 kit, it's pretty much explaining why he chose what parts, and so on....it will give you a good idea of what to expect.
Oh, and that aprticular kit speaker sounds pretty darn good, I use those as my main listening speakers, and love em.
but as far as building your own...buy the drivers first, then decide what you want your speakers to do, and be ralistic about it...then you have to go through all kinds of math involving the characteristics of the drivers to determine where and what slop your crossover will be, the size of your cabinet, and if your crossover needs baffle step compensation, etc. It's far more than slapping a 3-1/2" car speaker into a carboard tube and seeing how much bass you can get out of it (one of my early experiments as a kid...that woofer actually caught fire as I put nearly 200w through it).
Either way, if your willing to take your time, start off small, and experiment a bit. The smaller tang band drivers are fun for starters since they really don't need a crossover, so are good to experiment with box designs, and such. Then you can move on to something like Dayton components and playing with making crossovers to get them to paly nicely...dayton is low enough cost that you can buy lots of em and not anger the wife too badly.
...from there, the sky's the limit!