Hans, thanks for your answer [:)]

Mike, I think this size information would be useful in the catalog and in the furniture list. In the catalog, it will help users who wants to add only small models to their home. In the furniture list, it will help users to decide the items they should remove / replace first if they want to reduce the size of their .sh3d file.
In all cases, this additional column will be optional and will be displayed only if the user selects the matching item in the Furniture > Display column menu. By the way, this menu proposes the Level item which, I think, is the option you look for.