Vault intersection

Hi guys, any idea how i can make this shape? i managed to a few weeks ago but can’t get through it now. thanks!

My guess is that if you untrimmed the object you’d see the edges of the untrimmed surface, and that would give you the curves that you could use to do a Sweep2 to make it. The isocurves look more complicated than they need to be for that shape, so untrim may result in something surprising.