When going from a double or triple chainring to a singel one, you can buy short chainring bolts for about $10 or you can grind the ends of the long ones down. I have done both, but prefer buying the short ones. I like the chrome plated steel Sugino ones my LBS sells.
If you add up the cost of parts and tools you might decide to just buy a new bike. You can get a nice SS road bike from Specialized, Raleigh, KHS, or Redline for about $500. With the cost of the tools and your time, It mike make more sense to just buy one of these unless you are trying to do it for cheap or just want to do the work yourself. I think the payback for doing it yourself comes on the second bike when you already have the tools. Plus, I just wanted to do it myself for the fun of it. Building your own also means you are qualified to do your own repairs and maintenance. Might as well be self sufficient.