Building is a good idea, but any build will take a garage or dry space, tools, and the ability to get around to parts.. how big do you want the bike to be?
reliability & parts availability in relation to available bread are the #1 considerations..
how far from scratch do you want the build to be? (BTW, the rest of this rant assumes yer not talking about a kit build, but at least from the frame, up)
how much cash do you have to start with?
how much time?
how much experience do you have? ever do any tear downs, or top end work?
can you at least *completely* rebuild a lawnmower engine?
you do *not* want to lauinch on a cross country trip on your first homebuild of *any* kind, until you pace her to where she runsfault free around your homebase for a *minimum* of 300 miles..
& i mean *fault free*, unless you are an experienced mechanic who can diagnose & repair simple problems without much more than a few basic tools.
if you *do* do a build from scratch.. picking your frame, picing your motor/gearbox, doing your own wiring, brakes etc., *with no previous mechanical experience* and you have good counsel, figure about 300 hours, minimum, in the best of circumstances..less if you are being helped directly by a decent gearhead..
your first build will present you with more problems and questions than you can imagine..
at first they will seem like you are being cursed by the deamons of internal combustion design (which in fact will actually be the case), but you will gain knowledge & wisdom & self-reliability..
if your are doing this in a 'shade tree' enviornment, your first build, even if sucessfull, may self destruct after only several hundred miles..
you will have learned enough, however, to know what to look for in used vehicles & maintain them on the cheap, for prolonged periods..
if you can get a hold of parts for several of the same year & model bikes, & do your build from there, that is another proposition all together..
you will learn almost as much & you will have a lot more confidence..
the most practical approach, if you want to learn & build & take care of yourself while traveling is to find a bike & rebuild it..
consider your budget, what you want to do with it, the size you want & how much work you can realisticly do in your timeframe..
you can find good deals on plenty of bikes, especialy ones that need work..
remember that if you want good milage, manuverabilty & cross terrain potential, go for a low CC engine.
don't get a dirt bike, but get something you can push, for sure, if you want to do any moderate off-roading or stealth camping..
motorcycle traveling is fatuiging on smaller bikes, too, and requires some consideration of what your route will be like.. if you think you'll do anything in the desert, even if by highway, bring water.
bikes are not stable, so give consideration to your center of gravity when you pack.
if you're going to build to travel, make your racks low & easily removeable..
anyways.. good luck!!
C