Can the top floor of the masjid be made into an Islamic library?

الاستفتاء

We store extra articles of the masjid, such as fans etc. in the top floor of the masjid. Some people are suggesting that the top floor of the masjid be made into an Islamic library. Can the top floor of the masjid be made into a library? Secondly, is it permissible to perform the Maghrib, Isha, and Taraweeh Salah on the roof of the masjid in the summer, and the Zuhr Salah in the winter?

الجواب حامدا و مصلیا

Whatever area was given as Waqf to build a masjid will always be considered as the masjid from the ground and even what is above that, and designated for Salah and other forms of worship. For this reason, it will not be permissible to build a library on the top floor of the masjid. However it will be permissible to erect cupboards on the side walls or in the corner of the masjid for placing the Holy Quran and other Islamic books. As for establishing the congregational prayers on the roof of the masjid, if this is done simply because the weather is hot, then it will be Makrooh (disliked). However, if there is not enough space in the masjid to facilitate all of the worshipers, then it will be permissible to perform Salah on the roof of the masjid.