The Committee wants to hire out the top floor of the Musjid for weddings, etc.

Answer

It is not permissible to hire out the upper floor of the Musjid as a hall for weddings or for any other function whatsoever. The upper floor is in exactly the same category as the lower floor. It is part of the Musjid proper. Any activity which is not permissible in the lower floor is likewise not permissible in the upper floor. The space above the Musjid as far as the heavens has the same status as the Musjid.