To make the most out of Revit content, including improving its performance when placed within a project, families should generally be modeled at Revit’s three levels of detail in 3D views as well as 2D views (see previous posts for examples of content I’ve created as such).
I recently finished a project where among the families I did there was this CCTV monitor with a nested symbol. Starting from a face-based template, I created the base and the arm of the monitor and then created a couple reference lines to host the geometry for the screen. The family was generic and so I decided to allow the screen to be set to whatever size might be deemed necessary by the user. To that end, I figured the best way to set the size would be by entering the screen’s diagonal length in inches in an instance parameter. You can also tweak the ratio between height and width, but I left that as a type parameter. These are the parameters I created: