What is the ruling on purchasing an apartment through an Islamic bank at a price higher than its actual value, to include the cost of the roof and other expenses, with the buyer's knowledge? And what are the implications for the buyer in this case?

This transaction is forbidden because it involves collusion between you and the apartment owner, which leads to the bank paying you an amount (three thousand dinars) as the price for the roof and maintenance, which is not the reality. Consequently, this results in falling into usury, as the bank charges interest on this amount. Thus, it is one of the forbidden usurious stratagems.