What should a design change log include?

Reference and date make each change easy to find. The source links to the email or file that proves it.

Scope status says whether the change is inside the fee. Hours and fee effect turn a request into a price.

Notice date and approval status show what the client has been told and what the client has agreed.

Keep it in a shared file with one owner. Review it weekly and close each line when it is paid or dropped.