Technically it's not possible to have multiple angle roof sections and adjust them all seperately, the roof angle is a global change so it resets any odd angles if you move the slider once you've got them set up. It's a little hard for me to explain too so bear with me, it's a trick I picked up from TS2 building incase that helps.

Using this house as an example I started out by roofing the whole place with the roof styles I wanted, then I adjusted the angle until the left side roof was steep enough.

Once that angle was right I removed / deleted the left roof section (i.e. the one(s) with the correct slope angle) then set the angle for the rest of the roof, after that's done I just hit the "undo" button. It replaced the deleted portion of roof including it's steeper slope angle, but doesn't reset / change the rest of the roof angle.

It takes a bit of playing with especially for bigger roofing projects since you have to delete "correct" sections then adjust other sections before "undoing" the deletes, since deleting things that are right kinda goes against the grain when you're trying to create hehe