First fixed bike build thread - Help build my first singlespeed or fixed bike

Currently I have a bike that I bought last summer but now I want to make a new one and have no idea what so ever of what parts i'm looking for. After making up a thread of decided whether to buy the fuji feather or the bianchi pista, based on the replies i got, I decided to try and make one myself. Could anyone give me advice? Maybe post of up their projects and how much it cost them? If anything, any link to some guidelines would be great.

The purpose of this bike is to ride around London roads, it can be either fixed or single speed but must have atleast one brake. A flipflop hub is also prefered as so is a frame that is capable of having two brakes.

Preferences
Sizing - 52cm/54cm would fit me
Definatly a light bike
Drop handle bars are preferred
Thin tires
I've also been looking around the forum and found some security features some of the components have e.g wheels that are released using a different key
Price range £500-£700 or less if possible
In terms of looks, it's gotta look abit modern, as in something like this

Also, could you tell me what to avoid

Thanks