Obviously, the greater the amount of coverage, the higher the premiums.  You do not want to waste money on insurance, but you do want to carry enough so that your business can survive a lawsuit or natural disaster.

Be sure to carry enough insurance on the building to rebuild it.  There is no need to insure the total value of your real property (land & structures), because land does not burn.

If you are not sure how much it would cost you to rebuild, order an appraisal. (Be sure to get a rebuilding quote, not a quote on the sales value of the structure.)  Because the cost of rebuilding tends to increase over time, it is wise to get a new appraisal every few years.  Your insurance agent should be able to help you.

Basic fire insurance contracts cover the actual cash value of the structure, not its full replacement value.  But policies are routinely available with replacement cost coverage.  This is the coverage you want.