Trek Madone as fixie

you could buy the frame separately i'm sure.
for those with weight saving addiction this is the killer conquest, the holy grail, given the killer rabbit is not about or otherwise you have the holy grenade at hand :D

The lightest stock road frame you can buy is the Scott Addict @ 790g as opposed the 1070g for a Madone. Putting aside the fact that I shaved more than 280g off my all-up weight when I went to the toilet this morning, you need to ask what the objective of building this up fixed would be. If you want to go fast on the flat, being stiff and aero is at least as important (TT bikes aren't that light), if you are doing hill climbs then you can lose the weight getting rid of brakes, and chopping bits off you handle bars. If you want to do climbing (as in alpine stuff) then having a light bike is great, but fixing it screws you up on descents.