The roof plan has to be drawn. Sigh.
Update: I changed the recommended line weights, making them lighter. I think this will make the structure plan read better.
I've divided this process into two parts: Generating the lines, and editing the drawing so it looks good.
Generating the lines:
1. Set the layer combination to '1a. Shoot Roof Plan'
2. In 3D Window Settings (Cmd+Opt+1), turn the fills off. Set the mode to Hidden Line.
3. In 3D Projection Settings (Cmd+1), choose the roof plan view. Roll the camera around to the bottom (270).
4. 3D Window. OPEN YOUR EYES. Look for stuff sticking through the roofs. Make sure everything is showing that you want. Adjust layers if necessary. You can do roof-trimming and SEOs from this point of view, so have at it.
5. Activate the marquee tool and choose the flat geometry method. Draw a marquee around the area you want. (This will probably be everything you can see.) Copy. Check the 'Remove Redundant Lines' box.
6. Back to the Floor Plan window. Roof story. Paste. Drop it.
7. Find & Select for Lines on the ArchiCAD layer. Group the lines. Switch their layer to '+A Roof Plan Line'.
Now you've got a roof plan. It looks like !@#$%, but it's accurate and not totally useless. If a structural engineer wants a roof plan, this one is probably good enough. To finish it takes a few more steps.
(Note: If you have a site plan in your future, now is a good time to copy this material for that purpose.)
Editing and noting the plan:
1. Set the layer combination to '1: Working Floor+Roof Plan'.
2. Pretty-up the line weights. Don't change the lines that are there, just trace with the line or polyline tool. Outline the entire roof with pen 45. (Use an empty fill or a polyline for this.) Outline interior edges, such as the front and sides of a dormer, with pen 53. Change the remaining lines (hips, valleys, ridges) to pen 32. Of course you can you different colors with these weights. I recommend changing the color as well as the weight. Much easier to see what you've done.
3. Clean up intersections and other scraggly bits.
4. Use fills with an opaque background for the roof materials. Remember you must use the fill origin for these fills. It will take some sending backwards and forwards to get the gutters to hide properly.
5. For the slope arrow, use a line with an arrowhead at one end. The arrow points down.
6. Note the roof materials, gutters, crickets, etc.
OK now you're done.
The gutters themselves display on the roof plan. They should not be a part of the 3D pasted drawing. The gutters have their own layer for this purpose: F Gutter. Most gutters will be placed on the roof story. Those visible in the second floor plan should be placed there, then set to display one story above.
If you show or hide additional layers when generating the 3D view, remember to update the '1a. Shoot Roof Plan' layer combination. You will probably have to do the roof plan entirely over at least once (whine), and this will save you a step.