what is the maximum amount of flood insurance for commercial building you can get in florida?

It's the same everywhere. $500,000 on commercial buildings (non-residential) unless they are in an emergency program area inwhich it is $100,000. Contents are the same.

Here is a link to the Guidelines.

the reason i ask is because the insurance company for one of our customers that is in a flood zone said that the maximum is #350,000 for commercial building in the state of florida

Maybe for a private insurer...make sure the insurance company is isuing through the NFIP. There are onerous rules (in the guidelines) for private policies...attempt to stay away from those!