Problem with loft curves

Hello!

I'm just starting out with GH, trying to do my best at getting it. Right now I'm doing something that should be really simple: I have to meshes and I need to measure their "variation". To do so I create vertical contours and loft them to create the "area of variation". When I do it with a (-1;1;0) vector it works perfectly, but when I change it to (1;1;0) or (0;1;0) it doesn't show a desirable result.

I would really apreciate some help, I'm sure this will sound very basic to most of you,

Thanks in advance