I have managed to access load density parameter and check wether it read only or not using the below code.
Space_Element = UnwrapElement(IN[0])
Place your code below this line
doc = DocumentManager.Instance.CurrentDBDocument
TransactionManager.Instance.EnsureInTransaction(doc)
ParamN = Space_Element.get_Parameter(BuiltInParameter.ROOM_DESIGN_LIGHTING_LOAD_PER_AREA_PARAM)
ParamNST = ParamN.StorageType
ParamNSTV = ParamN.AsDouble()
check = ParamN.IsReadOnly
TransactionManager.Instance.TransactionTaskDone()
Assign your output to the OUT variable.
OUT = ParamN,ParamNST,ParamNSTV,check