Hi Diane,
change to one end's gable material seems to change both. I am making sure only 1 gable edge selection arrow is green before changing properties.
You are right on this one - I have never noticed before that this happened, presumably because normally all the gable ends would be the same (unless the wall was extending into the gable of course).
I can think of a couple of ways to get around it but the simplest may be just to 'cover' the gable end with a 'Triangle'. The attached BIM file has a collection of "Useful Shapes", some already available within TFP but most that I have made to cover various situations. Triangle1 should do what you want. You will have to resize it to fit, Elevate it (right click) of course and adjust the width and height to get the slope it fit but it should work although obviously not as easy as just changing the texture.
You may find some of the other shapes useful too for different things. To use them, just save the BIM file to your computer, go to File / Catalogues / Import BIM and follow the dialog box. The objects will be added into a 'Shapes' folder in your Interior Accessories. Once imported, you will notice that most of these shapes can rotated vertically also. Unless you have V16 it may complain about being from a later version, but it should still accept it if you persist. If not, let me know and I will post an earlier version.
Another alternative would be to create separate gables on a second location and position them a fraction lower and slightly in front of the main roof ones, so that the second gable surface in in front of the main roof one (or turn it off), but that could get messy too making sure the other parts do not show through the main roof.
Jack, Doug or others may have come across this before and have some other suggestions.
Re the Terrain Slopes tool. As with the Plateau, these also add to each other and they also extend across the whole terrain, so if you have three slopes at different angles, you could end up with 'steps' in the terrain at the sides. You may still find the Plateaus work best for multiple slopes.
They are fun to play with but essential to experiment first on a practice model!!

Allan