changing families' material ..

Hi,

i've downloaded some families ... some of them have no materials .. so, every time i try to change /add material to it .. it doesn't appear in the rendered image and all what i get is that dark gray default material ..

Welcome to the forums.
You will need to open the families and assign a material directly within the family or add a material parameter that will allow you to change the material from within the project.
This should get you started if you aren't familiar with how to assign materials. Post back if you have trouble figuring it out.
http://wikihelp.autodesk.com/Revit/e...3-Creating1313

You will definitely want to familiarize yourself with Component Construction which is apart of the family editor. A lot of that will delve into assigning a material parameter to a particular object within the component. Component blocks can be downloaded from anywhere (Revit City being a reasonable spot), however, you are at the original creator's mercy. You're best bet is to become familiar with the Family Editor portion (find some tutorials on the web) and address these areas while building whatever component you need.

Also, the simple answer could be that when rendering, make sure you are applying the changes to the rendering portion of that material properties as well. You may only be changing the attributes of that component in a certain detail view verses changes across all visible formats. For instance, in the library, you may select you want a wall to appear as brick, but that change only applies at the hidden lines and not on shaded or rendered properties. Maybe you want those bricks to be blue, and instead of Revit assuming this, it allows you to request it.