So Im thinking about building my first bike up from scratch, and I could use some help before i start hitting ebay for parts.

I already have a great bike that ive put some decent mileage on, and Ive done nearly all of the work on that one. I want to try to build a bike now, and I also want a fixed gear for my everyday/commuter bike, so that I can turn my current bike into a cross bike. Im not quite sure what I sould look for in a frame for a fixed gear, much less in the rest of the components (particularly the drivetrain).

I suppose my main question is what are the most important factors when looking for a fixed gear frame (keep in mind that I am probobly going to be on ebay for this)? My current frame is 53 and its pretty comfortable, I heard though that when dealing with fixed gear bikes, you should go down in size a bit... is that true?

I know very little about actual bike building, so any help anyone could offer would REALLY be appreciated. Im just not sure about where to get started on this project.

Thank a lot for any help that yall can offer.

-Seth