I received some help at the DAZ forums for Carrara and found out that my problem is that I've been deleting the cap (ceiling) from each of the rooms because I wanted to add some interior walls.  After adding them back, the different roofs are now do-able.

I was glad to hear from the creator of this marvelous add-on program.  I really like it, but the instructions (I'm sorry to say) aren't very thorough.  I jumped from Carrara 3 to 5 and there's a bit of a learning curve there as well.

Thanks again.  If I run into other difficulties, I will send them directly to you (Julian) along with the file.

Poser 2, 3, 4, 5, 6, 7, 8, 9, 10, Pro 2014, 11, 11 Pro