Hello, I am in the middle of creating some buildings for fun.
It all went great until i came to the roof, on this picture I used wedgecorners and gapfil, but as you can see it isnt perfect.
So i wanted to know if there is an easier way, a plugin or helpful tips.
Did you try to use regular wedges instead of GapFill? I tried recreating what you made using that.
Don’t use gap-fill for those stuff, as gap-fill does not account for 4 sided shapes lol (I think there was this equilateral fill or something plugin, its not called that but i THINK i’ve heard of it)
I did actually!
But for some reason when I duplicated a corner piece and used the move tool it didnt align (which was wierd because everything was in an 90* angle and It was a straight line it had to be moved it)
And apparently it got fixed by me deleting what i had and tried to redo it in the way you did it.
Still haven’t figured out what happened before though if it was a bug or smth, but I can see now that it wasn’t supposed to happen.
But nonetheless thank you for the answer! 
Sometimes when you copy and paste, parts will misalign. I dunno why it happens either, but it can be fixed using the select tool. Glad I could help!
