Tricky stuff 
import clr
clr.AddReference('RevitAPI')
from Autodesk.Revit.DB import *
from Autodesk.Revit.DB.Structure import *
clr.AddReference('RevitAPIUI')
from Autodesk.Revit.UI import *
clr.AddReference('System')
from System.Collections.Generic import List
clr.AddReference('RevitNodes')
import Revit
clr.ImportExtensions(Revit.GeometryConversion)
clr.ImportExtensions(Revit.Elements)
clr.AddReference('RevitServices')
import RevitServices
from RevitServices.Persistence import DocumentManager
from RevitServices.Transactions import TransactionManager
import Autodesk
doc = DocumentManager.Instance.CurrentDBDocument
uidoc=DocumentManager.Instance.CurrentUIApplication.ActiveUIDocument
ModelLines=UnwrapElement(IN[0])
CurveArray = CurveArray()
[CurveArray.Append(i.GeometryCurve) for i in ModelLines]
TransactionManager.Instance.EnsureInTransaction(doc)
Autodesk.Revit.Creation.Document
docCreation = doc.Create
sepLines = docCreation.NewRoomBoundaryLines(doc.ActiveView.SketchPlane, CurveArray, doc.ActiveView)
OUT = []
for i in sepLines:
OUT.append(i)
TransactionManager.Instance.TransactionTaskDone()