Here is one of those one's where you think, I wish there was an quicker way to do this, I wonder if I could "mirror" the "split surface line" and to my surprise it works.
After splitting a surface just select the "split line" and mirror.
In the roof (ridge cap) example split the two faces select the "split line" on the long plane select the "mirror-pick axis" select ridge. On the short plane select "split line" select "mirror-draw line" command draw mirror line mid point and perperdicular to ridge, and your done.
After splitting a surface just select the "split line" and mirror.
In the roof (ridge cap) example split the two faces select the "split line" on the long plane select the "mirror-pick axis" select ridge. On the short plane select "split line" select "mirror-draw line" command draw mirror line mid point and perperdicular to ridge, and your done.