Jorge- that's how I landed here to begin with! Chief will not allow multiple roof framing layers. It is possible to add a framing layer to the roof finishes, under the shingles, for example. I tried that, too. Shingles, plywood, fir framing, plywood. Chief morphs that framing layer into the actual framing layer, no plywood between, and generates one fat rafter- that's what I see in a framing view. In a cross section or full overview, the roof system appears to be floating by the height of the rafter.