Do you know the dimensions of the stall? What about the area in which he'll have turnout - do you know the approximate size/area, fencing type, etc of the turnout? This is all information you will want.
They want to be sure that the facilities are appropriate - they are looking for size/safety of all areas in which he will be to be certain that it is appropriate for him.
The stall, for example would be -- x by x foot stall, ..... walls (solid or partial), swinging door. The turnout description would be a x by x or xxx acre turnout, fenced with xxxx fencing (electric, mesh/field, barbed - certainly hope not, smooth, etc).
Anything you are not sure of, though, contact the facility you'll be keeping him at.