Mark3D

Chief architect has lots of training videos you need to watch them they are really helpful if your ssa is not upto date there is a lot on you tube as roofs can be tricky at first The walls you want to be gable, select the wall turn on gable with its toolbar also you can open the wall go to roof tab and set as gable.

See if that video gives you what you need

Does that get you what you need, check attached file I just finished it with manual roof. Working.plan

This video show what happens with overlapping height data

Also turn on attick walls there is one that messing with that intersection I found the problem went away when I deleted the attick walls if this is a suitable thing to do

To start with the file uploaded has no foundation so maybe its the wrong file, Jims screen shot show what to adjust.

Its seems to work fine for me, you are not changing the defaults instead of the individual garage rooms, or are you selecting the spanner after setting the negative height.

Try watching some videos there are heaps on you tube also chief website have more just not sure you can access them if you are using x15 may be SSA is not current. there is a note in the plan file attached plan file 264014205_3roofandporch.plan

Had a go its not perfect but maybe good enought with some manual editing 264014205_3roofandporch.plan

Steps to rotate

Watch this video https://www.chiefarchitect.com/videos/watch/10119/using-the-adjust-material-definition-tool.html

It is x17 only but x16 this should work

3D Menu-Adjust Materials-Interactive material Editor in standard camera view

it should look like =count*0.15 you are missing the zero before .15

Is this what you want blue house with porch roof help.plan