I want to close this cross vault in order to have a volume
cross vault.gh (25.2 KB)
You want to close it all the way down to the groundplane? Or just the bottom of the arcs? close it with vertical surfaces?
thank you, but i didn’t mention it. The volume is until the groundplane 
Look at your screenshot, You are missing information into the flip curve (yellow means warning)
yes that’s the point I couldn’t make the cross vault in the same way of a simple one… @Michael_Pryor
Use @HS_Kim solution, it is simpler for you. I do suggest you give this a read though, so you can understand some stuff. https://issuu.com/pabloherrera/docs/mode_lab_grasshopper_primer_third_e
That is basically what the other version is doing (except weave+loft instead of ruled) but there is is nothing in the flip curve in @immen.soussi screenshot
I’m not a professional in Rhino and gh and I’m trying to learn it for my thesis…
I did set multiple geometries and the 2 volumes are not like when it’s just 1 geometry
when it’s only one geometry, there is a detail that I notice in the final volume ( in the corner, the volume is not vertical and it doesn’t go until the 4 vertices)
thank you everyone, but the problem is not resolved until now
Why use Grasshopper? If you create 4 vertical planes from the sides of the rectangle that will be the base, make the planes taller than the cross vault, and then use trim or split to knock off what you don’t want. Add the base and join or union the parts and you should have a closed polysurface.