[Retric]

There’s a multitude of options here for various floor plans. One of the classic solutions is an external fire escape which is cheap per apartment and isn’t impacting floor space. People may dislike the aesthetics though.

Construction costs scale to the market segment you’re targeting. It’s common to aim up market with new housing but the cost of marble isn’t the same as the cost of housing. So be careful you’re looking at the minimums not what it takes to attract high end buyers.