good morning, 1 - I've been trying to figure out how to make an octagon roof too & haven't figured it out, I don't see any in that shape to start with 2 - when trying to place a room full of windows just to the left of the windows to choose from is a picture of a single window & a room, those will allow you to either place 1 or full room. 3 - the only thing I can think of is placing a small flat room & maybe it'll let you put a roof then ? There's a few things I don't like about the floors & how they work now..which goes into 4 - I haven't had any luck with that either, I've seen people say to make it into a room & then delete floor & then remove extra walls but it still wasn't working like I wanted.
Hope I was able to help a little. :)