If you need a finish material to carry up to a different elevation on one side from the other. There are a couple methods you can consider. One, using Edit Cut Profile, is a drafting exercise that doesn't affect the model itself. The other, using a custom wall setting for wall layers and Top Extension Distance, is a modelling exercise.
Tools menu > Edit Cut Profile is the "quick and dirty" technique. You simply slice off the portion of the finish you don't want to see in your detail section or callout view.
If you need to see this modelled then you can use the Top Extension Distance of a wall layer. You have to edit the properties of your wall type and preview the section of your wall. Then click Modify and select the top of one finish layer. A padlock appears. Unlock the padlock. This will permit this layer to be different than the other.
Note you cannot unlock both sides...
Now that the layer is "unlocked" you can adjust your wall in a section/detail view. Select the wall and open the Properties Dialog. Find the parameter: Top Extension Distance. Change the value to what you need it to be. Alternatively you can just select the wall and you'll find a small triangle control grip that you can drag up or down.
Once you are done with that you can finish up your detailing.
Note that this feature is disable when a wall is attached or if it is part of a Stacked Wall.