Is this room also used as a quiet room and/or a seclusion room? Because if it is only for restraints, then it is best located close to the nursing station. In my experience, most patients in the milieu do not want to be near a restraint /seclusion room.
Consider these factors:
What is the route of transport for the patient being accompanied to the restraint room?
If the route is through the nursing station or charting area or offices, and the patient is NOT in restraints while being escorted, then there is the chance that the patient might break free and access items that could be used to harm (self or others).
You need to be able to view AND hear the patient for the first hour if seclusion, and all the time if restraints. So staff proximity is important unless you have an inside-the-room camera. Even so, it the room is purely for restraints, then it needs to be W/I earshot, unless you have a dedicated sitter at all times.
Where I worked (I recently left) we reduced the use of restraints to -maybe-one every 14 months, prolly even less. We used seclusion and even that use went down. So I am not that familiar with restraints, and as such, haven't heard the term "restraint room" used in a long while. Can I make a suggestion - think about renaming the room to quiet room or seclusion room . Our patients hear a lot and the term restraint room can be frightening. I know I would be frightened if I heard it on the "other side" of the nursing station.
Caveat: Make sure your dimensions are the right height. Grilles/vents safely out of reach. I've seen this problem crop up before. Consult The Built Environment for Behavioral Health. Your Director of Maintenance and or Security should be able to access this BH physical plant guidebook, referred to by both the JC and the CMS.