V17 is an old program: current versions recognize the shape of walls (gable or straight) and develop the roofs accordingly.
Now, let's review some concepts, so you can visualize the concepts using the image attached
1 - TFP includes 2 types of roofs: Free Hand roofs (outlined and pointed in red color in the image attached) and roofs developed using the ready to used shapes (outlined in yellow color in the image attached). Note that the Autoroof feature creates Free Hand roofs (outlined and pointed in red color in the image attached).
2 - In order to edit a roof, change shapes, move or add points, the roof must be a Free Hand roof => this means a roof developed with the Autoroof feature or a roof created with the Free Hand roof tool (outlined and pointed in red color in the image attached).
3 - Therefore, in your case, you can create the gable roof using the Free Hand roof tool (outlined and pointed in red color in the image attached) or by editing an Autoroof, as explained in the item 4 (below).
3 - If you have a Free Hand hip roof (outlined in brown color in the image attached) and you wish to convert it to a hip roof, just perform these easy steps:
- Select and delete the end parts of the hip roof
- Select the point outlined in blue color in the image attached => move this point to the position outlined in green color in the image attached, following the path pointed with a magenta color arrow. Perform this action for the 4 points that created the hip in the original roof.
4 - Your hip roof is ready, as pointed with a black color arrow in the image attached.
TFP, as any program, has a learning curve. The best way to learn the program, IMO, is practice + practice + practice => Read and follow the manual (this is important), see the videos => try to create elements not related with your project, so you will become familiar with the commands and how to develop the different components.
If you are interested, I have several training e-books, one of them is free. See links below in my signature.