Definition for a Jāmi‘ Masjid
A jāmi‘ masjid is a masjid built in the city for the gathering of all residents of that city without being specific for a particular group of people.

To Make a Destroyed Masjid Najis
If a masjid had been destroyed or another building has been built in its place and there is no hope that the building of the masjid will be restored, it is not certain that it is ḥarām to make this place najis, although it is a caution not to make it najis.
 
To Sing a Song in a Masjid 
There is no objection to revolutionary martial chanting to the accompaniment of musical tunes in holy places on the occasions which warrant that provided that it does not go against the sanctity of the place or pose any nuisance to the worshippers and praying persons in such places as masjids. However, it is not at all permissible to play music which strays human being from the way of Allah.

To Play Music in a Masjid
The masjid has obviously a distinguished shar‘ī status. Therefore, if playing music is not appropriate to its status; it will be ḥarām even if the music is not ḥarām.

To Play a Game or the Like in a Masjid
One should avoid sports and any action which is not compatible with the sanctity of a masjid.

To Serve Food in a Masjid
There is no problem, in itself, in serving food to guests in a masjid. 

Entry of a Kāfir into a Masjid
According to shar‘, non-Muslims should not enter Masjid al-Ḥarām. If their entrance to other masjids is considered to entail disgrace and disrespect to the sanctity of the masjid, it is, also impermissible; rather, they should not enter any masjid.

To Destroy a Masjid
It is not permissible to change or to demolish a masjid unless there is an undeniable necessity.