I think I cracked how to form the roofs. Create editable splines that are extrude. Each shape is in the roof foot print. Then move the vertices up to the gable ends to form the pitched roof. Then to tidy up the intersections I used the slice method you described here. http://www.cgarchitect.com/upclose/article26_TB.asp (although I had to include an extra step to orientate the slice parrallel to the roof. I hope this method is clean and will not cause rednering issues when applying material at the intersections of the roof. Cheers Peter