We handle a tremendous number of transactions in Nassau County. There are 3 seperate Townships in Nassau County so the building code may vary. However, if a structure is more than 8" off the ground it would require railings and permits. Additionally, the hot tub is required to have an electrical certificate. You should visit your local building department for verification of the building code or you can contact an expediter to process all necessary permits. You may visit this site to find a local expediter in Nassau County: http://www.C21amhomes.com and click on Inspection Services on the tool bar.
I don't sell properties in New York, (but have an old college friend from Nassau County). I can put you in contact w/ a local area specialist since Alain Pinel Realtors belongs to the Leading Real Estate Companies of the World; a HUGE relocation network. They can help you with any permit/approval questions. Please email me directly for an excellent source!