As long as you use your common sense in the placement of staircase in the house whether outside or inside, it will automatically fall into applicable vastu. Vastu is about using common sense as per one's life style and not following blindly that was told in ancient times that was applicable to then life style when there was no gas, electricity or car or motorcycle in every house. That said, a staircase is a considerably bigger object to be placed in a house for the purpose of climbing to an upper elevation in the house. So what is essential is to make sure that it is appropriately placed without obstructing the aesthetics, air flow, without causing difficulties while climbing up especially. So it needs to be designed and placed wherever it would fit well as per the design of the house. The height of each step can maximum go up to 7.5 inches for making it easier even for older folks in the house and the width of each step must be atleast 9 or 10 inches. So the elevation has to be designed appropriately keeping this in mind as well.
