Problem I am not able to place a wall opening at a specific height since by default it's placed at the bottom of the wall.
Solution
Below is the workflow that needs to be followed in order to place a wall opening at a specific height
1. Place a wall in the model.
2. Then click on the Opening tool from the Architectural Elements tool group.
3. Next, define an appropriate Base Offset value in order to place the opening at the required height.