Hi,
the method AddValueString create the IfcGUID room parameter with the GlobalId value.
...
var room = document.Create.NewRoom(level, uv);
var globalId = '0oMylIW6P0kQ5Uj_5O3HgM'
Autodesk.Revit.DB.IFC.ExporterIFCUtils.AddValueString(room, new ElementId(BuiltInParameter.IFC_GUID), globalId);
...
Export as IFC File
#168= IFCSPACE('0oMylIW6P0kQ5Uj_5O3HgM',#41,'R025',$,$,#140,#164,'',.ELEMENT.,.INTERNAL.,$);
That's what i wanted.
Jo