As far as ANY major work done to a home it's Mandated to get permits, both communites have had some "unwarrented" work done on homes and it becomes a nightmare for the homeowner who purchase the home with additions with no permits.
Even if you pruchase a small ranch style home in these communities, your realtor MUST investigate the home for a "permit search" at the building dept. Just to be safe.
Phyllis McArthur DRE#01303020
Check with them them regarding permits, zoning, requirements, timetables etc.
When expanding it's always best to get permits for the work done, one, to make sure that things are done right and according to code, and two, to ensure higher market value later on should you decide to sell.
Costs will vary -- I always recommend you talk to at least 3 contractors who work in the area to get a clear picture of their plans, rates etc. The best price is not always the best option. Remember, you get what you pay for. The City of SSF may also be able to recommend some local contractors who they have dealt with in the past.