My design process is usually this (sometimes though; it just 'comes to me')...
1) Assess where the customer's bike is right now.
2) GRILL the crap out of the customer as to what they want out of the build.
3) Ask what the customer dislikes about their bike and why.
Using those three points, I try to mentally create a line and then extrapolate further than what they want to something they didn't even know they wanted... So far, I'm 100% successful.
![waytogo](http://ducatimonsterforum.org/Smileys/classic/waytogo.gif)