I found a method and now have wonderful 5mm solids from the faces 
lines = UnwrapElement(IN[0])
normal = UnwrapElement(IN[1])
loop = CurveLoop.Create(lines)
z= GeometryCreationUtilities.CreateExtrusionGeometry(List[CurveLoop]([loop]),normal,0.005)
OUT = z
Now i just have to find out if i can also get the area/volume of inbtersection when workin with Revit.DB.
Purpose is still that one:
Getting Faces and Solids gives errors for Walls and Floors - Dynamo (dynamobim.com)
Want to try to go the full Revit.DB route.