Maybe the answer is just in front of me but I have no time to think right now.
I want to make a 3d surface starting from a polyline. What I want to make is a tent, as in the attachment. The problem is that no matter what I do, I can't get a surface or even a very thin solid, I just get a 3d polyline.

Hi JTB - do you mean you want to fill in the top part of that shape?

You can use Construct/Sweep to do that. Start by selecting the curve out in front, like this:



Then run Construct/Sweep. In the upper-right corner, it will prompt you to "select one or two rails". Now select the other two curves and push Done. That will generate this shape:



Please let me know if that was not what you wanted to do.

- Michael

PERFECT!!! Thanks Michael.