National Flood Insurance Program Reauthorization and Improvement Act of 2017 This bill amends the National Flood Insurance Act of 1968 to extend the National Flood Insurance Program (NFIP) through FY2027. Every policy issued under NFIP must include documents describing the type of loss covered, a summary of the costs of the policy, and an explanation of the policy's parameters. The Federal Emergency Management Agency (FEMA) is directed to establish a program for "Write Your Own" companies (a company that writes and services federal standard flood insurance policies in its own name) to investigate preexisting structural conditions in properties. Participation in this program shall be voluntary. In the event a policyholder prevails in a lawsuit regarding claims against an insurance company or FEMA, the court may award litigation costs. Costs of an administrative appeal shall be awarded to a prevailing claimant. Engineers providing services in connection with NFIP must be certified by FEMA and be professionally licensed as an engineer. FEMA must establish a publicly searchable online registry of companies and individuals providing services related to NFIP. The bill establishes criminal and civil penalties for committing fraud or making false statements in connection with NFIP. The bill establishes whistleblower protections for individuals performing tasks related to NFIP, including federal employees, Write Your Own employees, and third-party administrators and service providers. It is unlawful for Write Your Own companies to violate the independence of a provider of engineering services in connection with flood insurance coverage. The Government Accountability Office must report on: (1) the effects of global warming on NFIP solvency, and (2) Hurricane Sandy claims handled by Write Your Own companies.