[Is It Permissible for a Contractor to Build a Mosque or School for Those Who Differ in Madhhab?]

Answer: If the mosque is a congregational mosque for daily congregational prayers and Friday prayer, the contractor ought not to enter into building it; for such a mosque would then be a center for propagating false doctrines and a center of invitation.
— If the intended mosque is for performing prayer without aiming at congregational and Friday prayers—such as small mosques built along roadways, and small neighborhood mosques—then there is no harm in building them, and no blame upon the contractor.
Source: Min Thimār al-ʿIlm wa al-Ḥikmah vol.2