Revit will make some great assumptions for you when you are creating you model. One of the assumptions which may not meet you exacting needs is the way Revit will automatically join the walls.
By default Revit will use a butt joint with the wall being more dominant at its start point, and less dominant at its end. The wall joint by display will automatically clean up the intersecting wall layers. You have various options to adjust how the walls join.
To modify the way the walls intersect, select the ‘Wall Joins’ tool (in the Modify ribbon) and select over the intersection in question.
In the Options bar you can change the configuration of how the wall intersects. The Previous / Next buttons adjust the Butt joint, the Miter (Mitre) option is a great way of having all finishes meet up on the corner, without any overlap, Square off allows you to join the walls at 90°no matter what angle they intersect.
You can also Change how the Join is displayed and whether you would like the join cleaned.
In the end, you don’t have to live with the Revit assumptions.
One last tip with altering a walls join, think about how the wall is joining in its entire height, the join at the bottom may not be the same as it is at the top.