If you're thinking to be 100% custom that you would start with a blank piece of paper, you would be correct. Perhaps you would have a better understanding if you went to the Newell website where they discuss customization.
Customization: Making Your Newell Your Own - Newell Coach
With the exception of their 'show coaches', they don't start construction on a Newell until the buyer has met with their team of designers and the coach has been designed.