wall & floor by face problem

[iffans]

I can't make a wall by face when I create a mass with spline or ellipse tools. I also can't make floor by face when the face is irregular form ( consist of spline, line, ellipse). Any explanation?

[sohocad]

I notice that if you do the spline massing in the vertical direction then I can add floor face but if I try to do it on plan than no luck?

refer attached....

[iffans]

Yes you right..
It's a little bit confusing right? What if I wanna make a corrugated roof from the mass I create? Maybe we need some better explanation from Revit moderator...:P