I have not used that add-on but what I do most of the time is model the roof the way it is built. I use one roof slab for the framing thickness, group them, copy them, changing the thickness to become the ply sheathing or other sheathing material. You can grab this new roof and move it up to lay on top of the structure roof plane. I model the fascia board with OBJECTiVE beam parts but you can use wall or beam sections from ArchiCAD as well. This takes a little bit of time but will give you the best representation in sections & elevations and once you have done it a few times it goes quickly. You can then extend the upper roof sheathing to line up with the outside face of your fascia boards which is how we build it here in Canada.
You can then add another roof layer on top of the sheathing which will be your roofing material. You can extend this past your fascia as you would do if you were building it.
Cheers,
Gerald
"The simplification of anything is always sensational" GKC
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