You are going to struggle to get a really smooth surface but there are a couple of ways.
First way would be to split the base priile at each of the 4 points you have shown.
Then split the 2 other curves where they intersect at the top.
You can then create surface using the 'Surface by Boudary' command.
Another way would be to split the base curve at 2 points - ie. at each end of the curve that you haven't shown a true view on. The one you have shown as a true view will be the path curve.
Then use the Blue Surf command using 3 cross-sections and one path curve.
You would define the cross sections in the order first base curve, cross curve, other base curve.
I will try and post an example tomorrow.
bc.
2.4GHz Core2 Quad, 4GB RAM,
Quadro FX4600.
Where would we be without sat-nav?