Hi urban_h - for several surfaces side-by-side like that it's best to use the Edit > Join command so that they are all connected together.

Once they are connected the whole thing will have one consistent normal direction which makes dealing with it easier. Also when surfaces are joined there is extra work done to ensure that they have the same mesh vertex structure along their shared edge, so that's another reason why you want to join things instead of leaving them as separate surfaces that just happen to be sitting next to one another.

It still may not necessarily have the right orientation that you want but at least the whole thing will be consistent as a single piece.

If you make a solid, then the generated mesh will automatically have the normals pointing towards the outside of the solid volume, but if your object does not form a solid MoI doesn't have any way of knowing if it's supposed to be the bottom piece of something or the top piece of something, so in that case the normal orientation is kind of arbitrary, it depends on various factors like possibly the directions you drew some of the initial curves and things like that.

Usually it is easiest to just turn on double-sided rendering in your rendering program and not really worry about what direction happens to be the positive normal side.

If you need to flip it, there is some more information on the Flip command here:
http://moi3d.com/2.0/docs/moi_command_reference10.htm#flip

- Michael