It is not advisable to renovate at your own expense a property that is not confirmed yet to be yours since you do not see it in the initial agreement with the management. The only way out to find out is to seek their advise and have a confirmation in black and white before proceeding with any works at all. You wouldn’t want to spend a hefty sum than be told later on to remove all the aftermath. Everybody welcomes that extra storage space but better to be safe than sorry.