Hey, Zephyr, here is what you can do. Chances are pretty good that the building is leased - generally speaking, large commercial properties fall into that category. IF that is true, contact the actual owners of the building and explain the situation honestly and that you are requesting their assistance to retrieve your expensive investment. Landlords typically have the right to enter their own property and can also delegate others to do so.
Here is how to check. Not knowing what town or city you are in - but assuming it is in the US - go to Google and type in the the name of the COUNTY that the city is in along with the name or abbreviation of your state, and the word taxes (example; orange county sc taxes). The resulting search will very likely reveal near the top the website for your county administration. Go to that website. There, you will very likely see a button or a tab for "online services," "taxes," "property search," or similar. There, you may be asked to click on some kind of acknowledgment for whatever - accept the terms, no worries - then you will probably be given a choice of searching by address or parcel number; choose address of course. Finally, you will see the data for the property (possible another click on Property Card will be necessary. Voila - there you will see the actual owner of the building and their contact information. I HOPE the owners are not the same doggone people, and you can go from there.
By the way, if the above method does not work, many counties also have "GIS Maps" where you can find the property and go from there. Now, you are an official detective AND can maybe get your drone back. If it is a Phantom, good luck to some guy who grabs it for his kid - he will not be able to register it with DJI or the FAA I bet.