Greg, I added manual roof planes to your 2nd floor. The roofs will cut the walls back on the third floor under the gables. I had to manually drag the attic walls over to fill the gaps left at the outside corners of the gable walls. You have several things going in this plan. Some of your exterior walls don't line up. The ceiling heights seem to be off. There doesn't appear to be enough room to add all of the cornice trim and corbels as shown in the pics. I had to raise the roof planes several inches just to get them where there are now. I believe you will have to raise them even more if you are going to add those cornice details. I didn't bother with any porch roofs, frieze boards, gable trim, etc. - you can add those. Also, I couldn't tell what was going on with the right side. The pics seem to indicate a small gable roof section over there - maybe over the balcony. Anyway, I "faked" a small gable section over it - may not be right, but you can adjust it if you wish. Also, I didn't mess with the box gutters you referred to; those could be added also.
Hope this helps, MikeAskod1-1017 Main St-modified.plan
Ridge_Runner's post in Cross gable roof was marked as the answer