I set the structural column first. Since the building is a 2-story building, wood frame would be enough to keep the building solid. I used the recommended size of wood column and beam.
For the first step, I drew the grid line according to the exterior walls existing. Then I added based on certain interior walls. Considering the max beam span, I added other gridlines to make sure the beams were not too far from each other.
After drawing the grid lines, I simply added the wood columns and beams according to grid lines.