Here’s something that may be correct but it’s really only a guess.
The side view that Shep shows is how the “cut dimension” is illustrated -Usually it is in an ortho projected view in a building section so you can see all the construction by cutting through it. The actual cut dimensions for rafters are not often given in the plans. That is for the carpenter to figure out, based on the plan view, pitch, overhang, type of material etc. In custom work such as timber frame barns, the dimensions of the framing may be given in more detail in the plans.
The outside dimension of the walls, measured in the horizontal, is usually what is shown on floor plans. If the dimension is to a post centerline or wall centerline instead, it should be clear on the plan.