Like building house, you need a plan. The house owner don’t draw the plan, but the architect did. Why? Isn’t that house owner the best person who know the best of his own house and what he wants?
See, the plan outlines how the house is built. It is a detailed engineering drawing which outlines more specifications in a format commonly understood by every contractors.
Website plan, in this case – should be done by a Web Design Architect, not the Owner.
It reduces dispute that always happen between web design companies and website owner. Both side failed to have the same picture, because the picture is not done correctly at first place!