Hi Massouh

Try these resources (I used all them in this image http://www.punchhelpers.com/residential14.html )

Say you have a wall with height 104", your wainscot height is 60" and your chair rail is 4"
1 - Create a wall with height= 64"--> apply the wainscot--> apply the rail as crown molding. For the upper segment, create a wall with height= 40"and set the elevation @ 64" (it will be stacked on the 64"wall)

or

2- Create a wall with height= 60"--> apply the wainscot--> For the upper segment, create a wall with height= 44"and set the elevation @ 60" (it will be stacked on the 60"wall)apply the rail as baseboard

Of course, you can create a rail using the 3D workshop and set it with the necessary dimensions / elevation

Patricia