How do I center angled walls?

[Jersey]

As in the attached, how do I center the point of this angled wall? I have tried using cad lines to create an exact location where the point of the wall should be, but when I draw the walls, I can't get it any closer than 1/4" at best. Then the walls above it, even when aligned, don't have exactly the same point. I won't even go into the problems I am having with the roof because of this. I think if I can get the walls right, I can solve the roof.