Model groups in Revit have a bad reputation. Many users avoid them completely. Indeed, they can be buggy.
However, they are still the best option when it comes to modeling repetitive interior layouts like apartments. This post starts with an overview of the tool. Then, you will get tips to have a smooth experience using groups.
BASIC PRINCIPLES OF CREATING GROUPS
Creating a Group
Select multiple elements. In the Modify tab, select the “Create Group” tools. Set a name to the group. You can then copy and paste the group.