Q 1: In
large graves were built for some Awliya' (pious people) and rooms were built over these graves with domes like those of Masjids (Mosque) attached over them. These Masjid-like rooms are dedicated by people for offering Salah (Prayer).
What is the ruling on that?
It is not permissible to build Masjids over graves, because this is a means leading to Shirk (associating others with Allah in His Divinity or worship). It is even more emphatically prohibited to offer Salah at the graves, whether in places built over them or not, as the Prophet (peace be upon him) forbade this. It leads to people calling upon the dead, seeking help and blessing from their graves. This is major Shirk which takes a person out of Islam. Accordingly, it is not permissible to offer Salah in such places, and rooms built over graves should be demolished, as the Prophet (peace be upon him) instructed
`Aly (may Allah be pleased with him)
Leave not a raised grave unleveled.
May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.