Hi Susanna,
I don't have an agreement template for you, but it's a great idea. I know of a core at Creighton University that was similarly "stuck" with some faculty equipment, but they never put anything in writing. However, that has caused a little drama, so I do think it's important to put something in writing that states: who is responsible for the instrument/keeping an eye on it/training users, what happens when you need the space back for the facility, how long the equipment can stay or how long until the agreement has to be reevaluated. Depending on what is expected of the core, you may want to reply to the faculty that you cannot provide the space to them for free, in which case, you would want to charge rent for the space and/or for "your management" in keeping an eye on the equipment. After all, core time and space aren't free.
I will add that faculty are notorious at finding "space" in someone else's lab that would be perfect for their equipment, but then they tend to forget that the equipment exists or expect the other lab to take care of it for them. It happened a couple times this summer where faculty walked through one of our cores, saw empty bench space, and asked if they could put something there. So actually, we should also consider developing some sort of template.
Anthony
Anthony S. Stender, Ph.D.
Microscopy Core Manager
Creighton University