I had to seriously consider the 2 routes, also. Buy a bike, or build up my existing "street bike".
I bought a used race bike, from someone I had grown to trust, and I can tell you I would have TERRIBLY REGRETED building my own. I'm not trying to convince you to do the same. But here are a few things I have found about my "race bike".
-- Some parts will not just "bolt on" - it seems as though there is a lot of "engineering" that goes into making the race components work.
-- there is a LOT of R&D type stuff that goes into making a solid platform, i.e. moving the forks up 2 mm to change the suspension and changing the valving on the rear to prevent squat, etc....
I guess my point is that I am glad that for my first bike that someone else had gone through all that learning curve and I can just look at the final result and learn from that. It also helps that my bike was built by Harley's suspension test engineer and others that work on motorcycles every day ;-)
However, if you do decide to build your own - there are tons of people out there to help you make decisions for spending your money!!! ;-)
Login to
http://www.nesba.com and poke around. They do track days and I have been very pleased riding with those guys. YOu get time on the best tracks in the country and they really manage things well for safety and learning.
Here are a few links (which i know from the region I'm in - not sure about NY)
http://www.learninngcurves.com/
http://www.trackaddix.com/
http://racemotorcycles.com/
Good luck!!!! and ask questions - some people live for helping the new guys out.