Write a Specification for your product ...
A Specification is usually a list of statements that tells the designer exactly what the product has to do and what the design requirements are.
Your Specification should include the following information about your product:
the main function of the product
the main overall dimensions of the product
the main materials that are likely to be used
an outline of the appearance of the product
special considerations or constraints of the users
details of the source of power, if needed
how anthropoetrics and ergonomics affect the design
the cost of the product
legal requirements that may have to be met
environmental considerstions and requirements