Thanks for the info; it matches the guidance I've already found.
The key point in your reply may be this sentence "Then if you sold this rental at a gain, you must show a gain on all assets, even if that gain is $1 on some assets. "
I initially entered zero gain for the roof, since I included all the gain in the house price. However, this just won't work. I'm going back to split it up and see if all the forms then populate correctly.
