I have created some roofs on AC17. Trying the edit-split into single plane roofs.. and it simply deletes my roof.. Is that a bug? There was not such a problem on older versions. Also I opened the file in AC16 and my roof also disappears after using this command. Now I'm not able to use Accessories for roofs..
Sorry, my bad. I have set 0 for roof thickness and the roof shows well like a polygons, but when trying to split, it disappears.