Dear Customer (name blocked for privacy),

This depends upon the terms of your lease. Most leases that allow occupant funded improvements, make the improvements the property of the owner of the building.

However, your improvements are sufficient enough, that you may be able to go to court to recover a portion of the investment. (The court would most likely apportion your improvements to a percentage of overall increase value to the property).

You need to begin with your lease. It will be difficult overcome terms of a lease which you signed, acknowledging your understanding.

Also, in regards to the terms of your lease, you need to see if it says anything about termination of the lease upon sale of the building. Without that, you might be able, with the help of an attorney, to invoke successor of interest rights. This means that you may be able to cause the new owner to honor the terms of the lease.