Check your lease. Depending on the improvements made, there is usually compensation to be negotiated based on the specific types of improvements in the form of lease rate reductions. Alternatively, YOU, the property owner are responsible for all maintenance, utility, infrastructure, etc. up keep. You should post on here what you spend on the building per year.
Now, what kind of a break would you give your tenant if they promised to fix leaks in the roof, maintain the parking lot, mow the grass, change filters, wash buildings, pay utilities, replace old door hardware, replace light bulbs, etc. I would bet you could give them an incredible break as the free and clear owner of a building that you didn't have to spend a dime on. What were you saying about improvements to your property?
That is all taken into consideration. However, their improvements become mine.