I need to create mark parameter in a family-based wall, whose value is not repeated in the project. To better understand, would be equal to the mark that exists in doors, which can not have duplicate values. It is also possible with the parameters of the family? Is there another solution for creating families? Shared Parameters could be the way?
The question is not clear enough. Revit will provide a Mark parameter to that wall-based element, once it is loaded in a project; therefore, it is not clear why you would need to create that parameter again. In addition, the Mark parameter does not guarantee that the value of Mark cannot be duplicated, as you said. That is just warning, only, that can be ignored.