A friend has 2 plots of land in an estate. He sought my opinion on whether to build a duplex or a block of flats. He likes duplex as a status symbol, but he thinks he wont be able to climb the staircase when he grows old. He likes the flats for commercial/letting out and making money. Friends, what advice should I offer him?

Block of flat, if commercial purposes are intended, I frankly feel that even for personal residence, duplexes are an unnecessary high cost, I have seen very beautiful and tasteful bungalows that beat some duplexes hands down...