Designing a family crest is pretty much up to you. Most are in the shape of a shield of armor, being neither round nor square. Most have the family name at the top or bottom, and many also include the family country of origin. But whatever you choose is up to you. Perhaps your family has a common long term interest, such as the men have always been bakers. A picture or design involving bakers could be at center. Perhaps input from all the family members would be in order.