You apparently have a property that is not very visible; large windows therefore make double sense. Building a balcony partly so that it could cast shade at certain times seems irrational to me. If you are also concerned about burglary, this would pose an additional risk, especially with windows/balcony doors potentially open in summer. Install an air conditioning system in the house for €10,000 - 15,000 and you will have the temperature under control. On some days it is warm in the bedroom here, maybe because we forgot to close the blinds, then the system runs very quietly or is set so that it is comfortable, a wonderful thing. We never set it as cold as in some buildings, but just cool slightly in summer so that it is pleasant; never again without! Before I would consider a balcony whose purpose I have to look for. If you had a special view from there of a cathedral, the old town, or something else, then maybe yes, but just like that is pure waste of money. We are all waiting for your building details to discuss this more concretely.