Factory rake

how does the motorcycle manufactures determine what they will use for the degree of rake on their bike? Would there be a problem with de-raking a bike ( less degrees at the head than choppering it out)?

If you derake your frame, you will reduce trail possibly making the bike unstable. If you both reduce rake and reduce the offset in the triple clamps, it is possible to maintain a safe amount of trail and have the advantages of reduced rake (quicker handling).

What fossil said. Aditionally, I doubt deraking the chassis is really worth it. If you put some taller shocks in the back and put an 18" tire in the front, it will most likely drop the rake enough without making the bike really unstable. You can make additional small changes by dropping the forks in the trees and tire choice front and rear. Remember you need ground clearance too.

For more on how changing the rake effects your bike read this article about "caster"

www.ozebiz.com.au/racetech/theory/align.html

this might help...
www.performanceoiltechnology.com/rake_and_trail.htm

and this is a pretty cool calculator, plus a clear picture for reference
www.rbracing-rsr.com/rakeandtrail.html