As a minimum include the unit size, the first part of your unit locations postcode (eg. BD2) and any special terms you wish to relay to the buyer (eg. a holding fee of £100 is payable upon collection and refunded when we are satisfied the unit is emptied). Also, you could include a brief list of what you see in the unit (but not essential).
Don’t forget to include what forms of payment you accept, eg. Cash, card, etc.