ᐅ Basement versus Increased Living Space on the Ground Floor

Dear all,

We are planning to build a bungalow with 3 rooms and about 85 sqm (915 sq ft) of living space. Since the plot is on a slope, we need to build with a partial basement.

Which option would likely be more cost-effective:

1. Living area on the ground floor (including a guest room) of 85 sqm (915 sq ft) and a 50 sqm (538 sq ft) basement used mainly as a utility cellar with a technical room (then we would only need one bathroom).

2. Ground floor only 75 sqm (808 sq ft), guest room in the partially finished 50 sqm (538 sq ft) basement as living space (which would require a second bathroom but could be fitted out later by ourselves).

As soon as the basement is meant to have living space, the access routes must be heated and insulated. Also, an internal staircase is necessary. A purely utility basement could possibly be accessed only from outside without an internal staircase, saving space.

Theoretically, a room on the ground floor requires about 12 sqm (129 sq ft). If this room is located in the basement, additional space for stairs on both floors and another hallway is needed, approximately 24 sqm (258 sq ft).

Am I thinking about this correctly?

Has anyone calculated a similar case before?