BAUM Ristretto 54

In general (if you were to get a custom frame):

• Geometry (how the fit data is translated into the design, to achieve desired handling charateristics).
  
• tubing selection, taking into consideration rider weight and desired comfort level
  
• aesthetics (proportions, paint, flourishes etc...)
  
  

Of course if you buy a bike made for someone else the first 2 points might be moot.