You have no legal obligation to be insured prior to the flights.
However, the Hands-On-Builder liability insurance has been especially designed for LAA members who build their own aircraft, whether they assembly a kit Aircraft or design their own experimental aircraft.
Through the stage of building an aircraft, you can cause an injury to someone or damage their property. This Hands-On Builder Liability insurance will cover the sums you will be legally liable to pay as a consequence of it.