It is narrated from Mahmood bin Labeed that when Sayyiduna Uthman (may Allah be pleased with him) intended to build a mosque, the people disliked it. Sayyiduna Uthman (may Allah be pleased with him) said: I heard the Messenger of Allah (peace and blessings be upon him) say: "Whoever builds a mosque for Allah, Allah will build for him a house like it in Paradise."
Hadith Referenceسنن دارمي / من كتاب الصللاة / 1430
The virtue of the one who builds a mosque is established from this hadith.
In another narration, it is stated that whoever builds a mosque for the pleasure of Allah, Allah Ta'ala will build for him a similar house in Paradise.
When Amir al-Mu’minin Sayyiduna Uthman ibn Affan radi Allahu anhu began the construction and expansion of Masjid al-Nabawi in 30 AH, some people did not approve of it. Upon this, Sayyiduna Uthman radi Allahu anhu presented this marfu‘ hadith and, with clear insight, expanded Masjid al-Nabawi. The meaning of “a similar house” is that just as a mosque has superiority over the houses of this world, likewise that house will have superiority over the other houses in Paradise. The intent is not that a house in Paradise will be exactly equal to the mosque.