I don't know if this is a me problem or a current game limitation
Converted the privacy fence to a brick wall, doors to metal doors, roofing I was having difficult with and resorted to building Small Metal Support to place roofing as the option to roof was not showing when I was trying to place it between a corner to get the "Must be supported on at least two sides" annotation with supports in place and without - probably not fully understanding how roofing works, but the sky light frames didn't give me any issues.
Completed the roofing to my knowledge, placed a large heater and it was not heating the room.
I am not sure if I haven't placed the roofing correctly, there is currently limitation with game in regards to building extensions or some reason I am not aware of
True, it is just one system in isolation.
I really thought the heater was an upscaled brazier that provided heat ( according to description + 10 modifier) in a consistent "flat 2D" radius with a dimishining return when it is in a closed air system and multiple heaters would provide accumalative effects where its radii meet.
The benefits would be greatly diminished ( to say a standard brazier) when a door or window was opened, regardless of how many were opened as the outside temperature would override the inside.
The roofing was a check to see if it was a closed air system, and made that assumption from all the times I got an open air type error when an building goes boom when a husk gets too close to something explosive.
I guess I am looking at the trees and not the forest. I don't expect anyone to do anything especially seeing as it is a complicated problem that has tendrils in a couple of other systems and still requires the optimisation to not physically set things on fire
Ultimately I have always wanted to make a building addition on my own and seems I got it right. So Half-Victory
Thank you for entertaining the idea even if I don't understand the technical game systems.