Total Cost of an ADU

[Doug Kienzle]

Going to build an ADU (800 total square feet) next to a house that has a basement and a second floor.

Question is, which costs more:

1) Building a second floor (roughly 400 sqft foundation and 400 sqft second floor).

Or

2) Build a basement (roughly 400 and 400 again).

I realize there are many factors (sewer slope in basement, soil removal, etc.), I was just curious about general cost (2nd floor wood vs basement concrete).

Any thoughts on the matter are greatly appreciated!