You'll have to talk to your local municipality, county, or whomever controls building permits in your area. Alternatively, you can hire a local civil engineer familiar with the requirements of your area.
I design a fair amount of houses in and around flood zones. In my area of Eastern VA and Eastern NC, I don't think there's a single municipality that allows fill in flood zones anymore. There are occasional exceptions, but for the most part the idea is that if you fill you just push the water elsewhere and make flooding worse for somebody else. So you may not be able to do it at all. Best to consult with an expert versed in local ordinances.