Hi krass, if you want to use Network the curves need to form a 2D regular grid. But in your case here in one of the grid directions you have one closed curve:



And the other curve in the same grid direction is an open curve:



For Network, the curves in one grid direction must all be either open or all closed, not a mix open and closed.

So to Network this you would need to split the closed curve into 2 pieces:


If you do that then it will be possible to select all the curves and use Construct > Network on them. But the quality won't be that great, you will get a kind of pinching effect where the network has its poles.

You'd probably get better quality if you made a blocky initial shape with multiple faces with sharp edges and then fillet rather than trying to construct it as just one single surface.

- Michael