Such an open ended question, kinda makes it hard to asnwer.
Check
this thread for some absic information.
Know this; once you start building stereo systems it can get very addicting very quickly. Someday mine will be redone for a third time and each time runs somewhere in the 3-5K range. The next redition should run somewhere in the 7k range, and that won't even stop people at alot of shows. Some of the real show stopping system that I see run well into the 10's of thousands. I've also had the privilage to do a little work on a $35k system. The guy ripped it all out 6 months later, said he wanted it bigger, better, and louder.