I would reckon it is almost similar to renting out your unit i.e. tenancy. Oh by the way, I only advise on the proper way of doings things.

First and foremost, check your Deed of Mutual Covenant or house rules and then the management in relation to such arrangement.

Once you get the green light, you may proceed to draw up your paper work.

You should prepare the letter. I don’t think it’s really complicated but it should cover amongst other things:-

(a) duration
(b) rental (yes, most importantly)
© deposit to secure obligation
(d) your obligations and
(e) termination