The best way to create a coping is to use a "wall sweep".
A "wall sweep" is a "system family". That means that you cannot create it as a standalone file, it is already loaded in the project file and it cannot be removed. However, it can be duplicated and configured to create different "wall sweeps" with different forms to fit your needs. You can find the command under the "wall tool" by developing the list of the tool.
In order to be customized, a "wall sweep" family uses a "profile family". The profile family is a "loadable family" (a standalone file) that you can create using a "family template" provided with Revit in the template folder. You can give the profile any form you wish but it has to be a closed form in order to work.
So after creating the "profile family" just load it in the project, duplicate the existing out of the box "wall sweep" and use your custom profile you just loaded to customize the duplicated system family.
Then you have to go to a 3d view, invoke the command of the wall sweep and click on the face of the wall you will like the coping to be. As you will see the profile of the wall sweep, extrudes to fit the total length of the wall and miters at the corners with the wall sweep of the next wall.
The wall sweep can be placed only on a wall face. In order create a coping(normally located on the top of the wall) you will have to put the wall sweep the highest possible on the exterior wall face and probably modify the profile to have its insertion point underneath it to have the coping located on the top of the wall.
Hope it helps
