I run my own custom paint and model railroad design business. On occasion I get asked to build my designs. The process generally involvs sitting down and determining the customers needs, what style of control they are wanting, and what they are wanting in return for their investment.

It is my suggestion to have everything in writing. This provides a defense and covers you should the customer later decide to back out. My policies for model Railroad desing and custom painting are posted on my web site Feel free to read them.
http://w3.trib.com/~mrljim/designpolicy.html http://w3.trib.com/~mrljim/paintpolicy.html

This should give you a little insite as to what to consider so as to protect your self should you need it.

If you have any further questions, please feel free to email me.

James