The forum is your friend, use it as such 
To find this post I simply searched for the method you are using: NewFootPrintRoof.
import clr
clr.AddReference('RevitAPI')
from Autodesk.Revit.DB import *
from clr import StrongBox
clr.AddReference('ProtoGeometry')
from Autodesk.DesignScript.Geometry import *
clr.AddReference("RevitNodes")
import Revit
clr.ImportExtensions(Revit.Elements)
clr.ImportExtensions(Revit.GeometryConversion)
clr.AddReference("RevitServices")
import RevitServices
from RevitServices.Persistence import DocumentManager
from RevitServices.Transactions import TransactionManager
doc = DocumentManager.Instance.CurrentDBDocument
uiapp = DocumentManager.Instance.CurrentUIApplication
app = uiapp.Application
uidoc = uiapp.ActiveUIDocument
outline = IN[0]
level = UnwrapElement(IN[1])
roofType = UnwrapElement(IN[2])
footprint = CurveArray()
for o in outline:
footprint.Append(o.ToRevitType(True) )
TransactionManager.Instance.EnsureInTransaction(doc)
# A strongbox containing a modelcurvearray
roofCurves = StrongBox[ModelCurveArray](ModelCurveArray())
New_Roof = doc.Create.NewFootPrintRoof(footprint, level, roofType, roofCurves)
TransactionManager.Instance.EnsureInTransaction(doc)
OUT = New_Roof
This code takes in the curves from Dynamo, extracted from the walls. If you wanted to take the geometry directly from the walls you would have to tweak it but I’m sure you can use the forum to help you get that :).