Your question is still a little vague. Do you mean you want to build your own speaker cabnets? Or do you mean you want to build your own package of speakers in a set to buy?
Wellll,
I am assuming you want the cabinet to be part of the "kit". If that is the case try www.zalytron.com for a pretty good selection. Also, www.northcreekmusic.com If you want to try building your own enclosure that would mean a lot more choices.
www.gr-research.com - I have their Paradox 1. You also need to specify your budget, because "put together your own high end speaker" can mean lots of things to lots of people. The Paradox 1 kit, for instance, costs about $500/pr, and includes a cabinet, so all you do is solder/screw/sand/stain.
www.madisound.com also has great kits. I have built the Vifa center. The cabinet was high quality and it sound pretty good (for $200 you can't get better).