Roofs won't join

[ron.sanpedro]

Trying to do cruciform gables (four square gable) and running into trouble. It has been a while, but I am pretty sure the last time I did it I did it like a dormer. One gable runs the full width and length (both being equal), then another roof runs half way and perpendicular, and is then Joined. That then gets mirrored about the first ridge.
I tried a Roof by Footprint and Roof by Extrusion, and both error, with no useful information. And yet the preview you see in the error dialog looks right!
I guess it has just been a while that I have been doing roofs with parapets. What am I doing wrong?

Thanks!
Gordon

[patricks]

Do it as a roof by footprint, but use slope arrows instead of slope-defining lines. You'll probably need to split each line at the midpoint, then place 8 slope arrows along the lines, each pointing from the corner to the middle. Set up the slope values are required and you'll have your 4-gable roof.