How much are you going to spend and if it was me, I'd start with Craigslist and find a decent single speed. Buy it, ride it then figure out what you would want different and start making a list. Ride others peoples bikes and note what you liked and what you didn't like. In the end, you might just build your own, you'll meet new people with your interests and heck, one of them might even help you build one or sell you theirs.

Don't rush into anything, buy cheap, ride cheap then decide what want.