Mike,
Thanks for your reply. However I have tried and retried this method and keep getting the same results as follows.
I draw two rectangles at rightanges to each other then overlap them to create the basis for the intersecting roofs. I then draw a polygon over the part of the secondary roof that is to remain, cut, select the primary roof, edit group, paste in place, exit group. That works, i get a neat cut-out in the primary roof where the secondary roof intersects.
I then draw a polygon over the remaining part of the secondary roof, cut, select secondary roof, edit group, paste in place, exit group.
That doesnt work. Each time i try it only removes one roof slope of the two sections (gabled roof or one of three if left as hipped). Each time i re-enter the secondary roof group, the part of the roof that remains, has somehow come to the front, over the polygon, whilst the the section that was removed has remained behind the polygon. By sending the roof slopes behind the polygons, they are once again covered by the polys, then on exiting the group it reverts again. Every time it keeps sending all but one roof face back up to the front, covering the polygons. Most frustrating. What am i doing wrong?