Create new Form element by Loft operation, and add it into the Autodesk Revit family document. 
   Namespace:   Autodesk.Revit.Creation  
  Assembly:   RevitAPI  (in RevitAPI.dll) Version: 2015.0.0.0 (2015.0.0.0) 
Syntax
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Parameters
- isSolid
 -  Type:  System Boolean  
Indicates if the Form is Solid or Void. 
- profiles
 -  Type:  Autodesk.Revit.DB ReferenceArrayArray  
The profile set of the newly created loft. Each profile should consist of only one curve loop. 
Return Value
If creation was successful form is are returned.Examples
private Form CreateLoftForm(Autodesk.Revit.DB.Document document)
{
    Form loftForm = null;
    ReferencePointArray rpa = new ReferencePointArray();
    ReferenceArrayArray ref_ar_ar = new ReferenceArrayArray();
    ReferenceArray ref_ar = new ReferenceArray();
    ReferencePoint rp = null;
    XYZ xyz = null;
    // make first profile curve for loft
    xyz = document.Application.Create.NewXYZ(0, 0, 0);
    rp = document.FamilyCreate.NewReferencePoint(xyz);
    rpa.Append(rp);
    xyz = document.Application.Create.NewXYZ(0, 50, 10);
    rp = document.FamilyCreate.NewReferencePoint(xyz);
    rpa.Append(rp);
    xyz = document.Application.Create.NewXYZ(0, 100, 0);
    rp = document.FamilyCreate.NewReferencePoint(xyz);
    rpa.Append(rp);
    CurveByPoints cbp = document.FamilyCreate.NewCurveByPoints(rpa);
    ref_ar.Append(cbp.GeometryCurve.Reference);
    ref_ar_ar.Append(ref_ar);
    rpa.Clear();
    ref_ar = new ReferenceArray();
    // make second profile curve for loft
    xyz = document.Application.Create.NewXYZ(50, 0, 0);
    rp = document.FamilyCreate.NewReferencePoint(xyz);
    rpa.Append(rp);
    xyz = document.Application.Create.NewXYZ(50, 50, 30);
    rp = document.FamilyCreate.NewReferencePoint(xyz);
    rpa.Append(rp);
    xyz = document.Application.Create.NewXYZ(50, 100, 0);
    rp = document.FamilyCreate.NewReferencePoint(xyz);
    rpa.Append(rp);
    cbp = document.FamilyCreate.NewCurveByPoints(rpa);
    ref_ar.Append(cbp.GeometryCurve.Reference);
    ref_ar_ar.Append(ref_ar);
    rpa.Clear();
    ref_ar = new ReferenceArray();
    // make third profile curve for loft
    xyz = document.Application.Create.NewXYZ(75, 0, 0);
    rp = document.FamilyCreate.NewReferencePoint(xyz);
    rpa.Append(rp);
    xyz = document.Application.Create.NewXYZ(75, 50, 5);
    rp = document.FamilyCreate.NewReferencePoint(xyz);
    rpa.Append(rp);
    xyz = document.Application.Create.NewXYZ(75, 100, 0);
    rp = document.FamilyCreate.NewReferencePoint(xyz);
    rpa.Append(rp);
    cbp = document.FamilyCreate.NewCurveByPoints(rpa);
    ref_ar.Append(cbp.GeometryCurve.Reference);
    ref_ar_ar.Append(ref_ar);
    loftForm = document.FamilyCreate.NewLoftForm(true, ref_ar_ar);
    return loftForm;
} Private Function CreateLoftForm(document As Autodesk.Revit.DB.Document) As Form
    Dim loftForm As Form = Nothing
    Dim rpa As New ReferencePointArray()
    Dim ref_ar_ar As New ReferenceArrayArray()
    Dim ref_ar As New ReferenceArray()
    Dim rp As ReferencePoint = Nothing
    Dim xyz As XYZ = Nothing
    ' make first profile curve for loft
    xyz = document.Application.Create.NewXYZ(0, 0, 0)
    rp = document.FamilyCreate.NewReferencePoint(xyz)
    rpa.Append(rp)
    xyz = document.Application.Create.NewXYZ(0, 50, 10)
    rp = document.FamilyCreate.NewReferencePoint(xyz)
    rpa.Append(rp)
    xyz = document.Application.Create.NewXYZ(0, 100, 0)
    rp = document.FamilyCreate.NewReferencePoint(xyz)
    rpa.Append(rp)
    Dim cbp As CurveByPoints = document.FamilyCreate.NewCurveByPoints(rpa)
    ref_ar.Append(cbp.GeometryCurve.Reference)
    ref_ar_ar.Append(ref_ar)
    rpa.Clear()
    ref_ar = New ReferenceArray()
    ' make second profile curve for loft
    xyz = document.Application.Create.NewXYZ(50, 0, 0)
    rp = document.FamilyCreate.NewReferencePoint(xyz)
    rpa.Append(rp)
    xyz = document.Application.Create.NewXYZ(50, 50, 30)
    rp = document.FamilyCreate.NewReferencePoint(xyz)
    rpa.Append(rp)
    xyz = document.Application.Create.NewXYZ(50, 100, 0)
    rp = document.FamilyCreate.NewReferencePoint(xyz)
    rpa.Append(rp)
    cbp = document.FamilyCreate.NewCurveByPoints(rpa)
    ref_ar.Append(cbp.GeometryCurve.Reference)
    ref_ar_ar.Append(ref_ar)
    rpa.Clear()
    ref_ar = New ReferenceArray()
    ' make third profile curve for loft
    xyz = document.Application.Create.NewXYZ(75, 0, 0)
    rp = document.FamilyCreate.NewReferencePoint(xyz)
    rpa.Append(rp)
    xyz = document.Application.Create.NewXYZ(75, 50, 5)
    rp = document.FamilyCreate.NewReferencePoint(xyz)
    rpa.Append(rp)
    xyz = document.Application.Create.NewXYZ(75, 100, 0)
    rp = document.FamilyCreate.NewReferencePoint(xyz)
    rpa.Append(rp)
    cbp = document.FamilyCreate.NewCurveByPoints(rpa)
    ref_ar.Append(cbp.GeometryCurve.Reference)
    ref_ar_ar.Append(ref_ar)
    loftForm = document.FamilyCreate.NewLoftForm(True, ref_ar_ar)
    Return loftForm
End Function