I have found that some Insurers are willing to look at the wider picture before assessing this. For example, if you were taking over an empty shop unit to renovate it and have it open as a hairdressers within 4-8 weeks, then they may offer you a full salon policy with some restrictions in the cover for the 4-8 weeks due to the unoccupancy. However, if you are only looking to insure the empty building whilst it is being renovated, without the full business insurance policy once you are open for business, you may find this harder and more expensive cover to get. This would definitely be classed as unoccupied cover.
Speak to your local insurance broker who will know the market dependant on your exact circumstances - never look for this type of insurance on the internet as there are far too many pitfalls.