The imaam being raised from his congregation during prayer
Question: Is there any effect on the validity of the prayer whereby the imaam is praying (leading) the prayer from a raised platform to the congregation of followers?
Response: There is (some) detail (to this issue); If the imaam was on his own, then it is permissible for him to be slightly raised such as the (height of the) stairs on the pulpit, (as) the Prophet (sal-Allaahu `alayhe wa sallam) ascended the pulpit and prayed (led the prayer) and then descended, so there is no harm in a slight raise so long as the imaam is on his own.
However, if there was a considerable raise then it is not permissible for the imaam to be singled out (like this) from the congregation of followers.
If however, the imaam was with (some of) the congregation of followers, then there is no harm in them being considerably raised (from the rest of the congregation of followers), so it is permissible for example that the imaam (and some of the congregation of followers) is on a higher level/floor and the rest of the congregation of followers are on lower levels/floors below him.
Shaykh Saailh ibn Fowzaan
al-Muntaqaa min Fataawa Shaykh Saalih al-Fowzaan – Volume 5, Page 58, Fatwa No.87 fatwaonline.com