Praise be to Allaah.
There is nothing wrong with this so long as (the apartment) is separate (from the pipe). Al-Imaam al-Muwaffaq, the author of al-Mughni and of al-Sharh al-Kabeer, said: It is permissible to use the area above the roof of the pipe and similar places, because the pipe is beneath and there is a roof over it. It is not allowed to pray in toilets and similar places, but according to the correct view, it is permissible to pray and read Qur’aan on the roof over them, as we have stated above. Some scholars said that it is not permissible to do that, but the correct view, in sha Allaah, is that it is OK. And Allaah knows best.