Edges between floating vertices?

[Philippe Hurbain]

Ah, I didn't got what Willy wanted. If indeed the purpose is to create a wall surface around an existing top surface, Gerald method is right. See also this very old tutorial http://philohome.com/isecalc/yttut.htm (but of course use more modern tools!), or this more modern one: https://www.wiki.ldraw.org/index.php?tit..._shape_one (granted, a bit different: since the top here is not flat, we must use projection on plane in ytruder instead of translation by distance).