If you are building new, you will be required build the house up in elevation to at lease the area's base flood elevation (BFE) as determined by FEMA. 

You should also never go to a GC with just elevations and a site plan.

even if the buildings were free, wouldn't always make sense. office has a deep floor plate, plumbing, firewalls, elevators, amenities are all huge costs to conversions.

I like to find elevated foundations, brick and hardwood, stone windowsills, built in wood features, a general overkill on construction materials...

You mentioned you can do this before a client makes an offer - do you visit the place or go by elevation? 

Especially on vertical surfaces, or you will have problems with runs/drips.In other words, do not lay them down like this...Elevate them on something like this...I learned the hard way!

A couple weeks go by and they ask for an elevation certificate so they can get an estimate on flood insurance.

It’s the stairs up to the top and the elevator down.

its not based on per unit...its based on size, location to the ocean, bay, US-1, 95, etc. as well as replacement value...hurricane windows, new roof, elevated access points, etc. all make for lower costs..Like my listing for a 4 unit building in miami Beach..we have full impact windows and all the front doors are up 3 steps except 1. so we have really good coverage for under $10k/year. other buildings pay $7k and don't have flood or have very low coverage. 

It was basically a 20 acre scree field at a 30 degree angle at 10,000 feet in elevation.