This is a python script for Dynamo that allows you to collect all model elements in a Revit model.

GetModelElements.py

#license https://choosealicense.com/licenses/bsd-3-clause/
import clr

# Import DocumentManager and TransactionManager
clr.AddReference("RevitServices")
import RevitServices
from RevitServices.Persistence import DocumentManager

# Import RevitAPI
clr.AddReference("RevitAPI")
import Autodesk
from Autodesk.Revit.DB import FilteredElementCollector

# our current document and model elements
doc = DocumentManager.Instance.CurrentDBDocument
allElements = FilteredElementCollector(doc).WhereElementIsNotElementType().ToElements()

# lists to use for results, faillist is if we ever need it
modelElements = []
failList = []

# iterate through the elements and see if it has model characteristics
for i in allElements:
	try:
		if i.Category.HasMaterialQuantities:
			modelElements.append(i)
	except:
		failList.append(i)
# output the model elements
OUT = modelElements