It’s up to you to decide the sums insured, and the type and level of cover that you want to take out. People generally want enough insurance to cover the property’s estimated replacement value. If you don’t have enough cover, you could end up having to cover some of the costs yourself.
Remember, Allianz will only pay up to the amount of your loss or the sum insured, whichever is the lesser - so you should also be careful not to over insure.