It is disliked for the imam to be at a higher place than the followers.
Abu Mas’ud al-Ansari says: “The Prophet sallallahu alehi wasallam prohibited that the imam should stand on something higher than the people behind him.” This is related by ad-Daraqutni, while al-Hafez is silent about it in al-Talkhis.
Hamam ibn al-Harith relates that Huzhaifah led the people in prayer in Mada’in (Iraq) and he stood on a bench. Abu Mas’ud pulled his shirt with a strong grip. When he finished his prayer Abu Mas’ud said: “Do you not know that this has been prohibited?” Huzhaifah said: “Certainly, I know it. I remembered it when you pulled me.” This is related by Abu Dawud, ash-Shaf’i, and al-Baihaqi. Al-Hakim, Ibn Khuzaimah, and Ibn Hibban grade it sahih.
On the other hand, if the imam has some reason for being higher than the followers, the act is not disliked. Sahl ibn Sa’d as-Sa’ady says: “I saw the Prophet sitting upon the pulpit on the first day that it was set up. He made the opening takbir while he was upon it and then he performed ruku’. Afterward, he moved behind the pulpit and made sajdah at the foot of the pulpit. Then, he repeated the same. When he had finished, he tumed to the people and said: “O people, I did that for you to follow me and to teach you my salah.”‘ This is related by Ahmad, al-Bukhari, and Muslim.: It is permissible for the followers to be at a higher place than the imam
Sa id ibn Mansur, ash-Shaf’i, al-Baihaqi, and al-Bukhari, in his comments, relate from Abu Hurairah that he prayed at the top of the mosque while following the imam. Anas used to pray in the room of Abu Naf’i to the right of the mosque and the room was his height’s high and its door faced the mosque of Basrah and Anas would pray in it, following the imam. The companions did not say anything about it. This is related by Sa’id ibn Mansur in his Sunan.
Ash-Shaukani observes: “If the follower is extremely high above the imam, for example, three hundred lengths, and he could not know what action the imam is doing then it is prohibited by consensus whether he is in a mosque or somewhere else. If it is less than that, it is permitted on the principle that unless proved otherwise a thing is permissible. This basis is supported by the above mentioned act of Abu Hurairah to which no one objected.”