It depends on what you want the bicycle for..
What beyond fashion or fitness could anyone that doesn't ride a velodrome want a fixed gear bike for?
As far as I'm concerned, if a person wants to know our opinion on fixed gear bikes and in the same breath wants parts priced so he could build his own, he's not ready for fixed. At this point I'm not sure he's ridden even a single speed bike and those are challenges in and of themselves on anything aside from prairie-flat roads. The best advice I as a person who's more or less in his shoes can offer is to start with a single gear freewheel and ride that for awhile before converting to fixed (if not foregoing fixed altogether). He mentioned that in his opening post, but for some reason he's "fixated" on the fixed gear aspect of a bike capable of both single speed freewheel and fixed.
I say fixed is for advanced riders for several reasons. One of them is clear: if he needs to make a quick change of direction and he leans his bike over too far, he'll probably end up low-siding if he pedal hits the ground.
Secondly, steps hills are pretty perilous for fixed gear bikes. As fast as a decline propels you is as fast as your legs are going to go. One had best have good knees to take that kind of punishment. Another thing is, it seems to be fashionable to ride fixed gear bikes without hand brakes. To an experienced rider that won't pose much of a problem -- in fact it's the order of the day for the hardcoe -- but for someone just starting out on fixed, having no brakes ought to be out of the question.
- F