Test01 for 6x6 timber

 See the previous post for calculations comparing 2x4", 6x6", and 8x10" framing.

qty - 40ct 6x6" timbers on 4' centers - 36' x 24' two floors - 9.5' ceilings

40qty 6x6" pine timbers, 26' long, set on 4' centers

Replacing the outer posts with structural foam create will reduce the number of posts by 30. Only 10 interior posts are required. I've drawn the foam create wall 1' thick. That can be adjusted to suit the structural load required. Also, the attachment for floor joists isn't known.

The ceiling heights are taller than necessary. This is just a test to estimate materials. See the previous post for calculations.