It tells you about powering, safe loading, flotation, ventilation, fuel systems, electrical systems, capacity, and much more. Cold hands do poor work. Besides, most glues do not set at low temperature. Do not make major changes in the design. In fact, DO NOT make any changes unless you discuss them with the designer.
Every detail has a reason.
You will be happier, longer. Study the local boats and boating conditions. Talk with local boat owners. You do not want a deep- keel boat on Maryland's Eastern Shore, etc. If possible, make your hardware rather than buying it.