who constructed it?
Either Umar ibn al-Khattab, the second caliph of the Rashidun Caliphate or Mu'awiyah.
Al-Aqsa Mosque
The current construction of the al-Aqsa Mosque is dated to the early Umayyad period of rule in Palestine. Architectural historian K. A. C. Creswell, referring to a testimony by Arculf, a Gallic monk, during his pilgrimage to Palestine in 679–82, notes the possibility that the second caliph of the Rashidun Caliphate, Umar ibn al-Khattab, erected a primitive quadrangular building for a capacity of 3,000 worshipers somewhere on the Haram ash-Sharif. However, Arculf visited Palestine during the reign of Mu'awiyah I, and it is possible that Mu'awiyah ordered the construction, not Umar. This latter claim is explicitly supported by the early Muslim scholar al-Muthahhar bin Tahir.
the distance between the western wall and the dome of the rock is approximately UNANSWERABLE what is the significance of this wall? It is the holiest place where Jews are permitted to pray and the Foundation Stone - the most sacred site in the Jewish faith - lies behind it. For Muslims, it constitutes the eastern border of "al-Haram al-Sharif", the Noble Sanctuary of the Al-Aqsa Mosque. what are the other different names it has? It was called as "Wailing Wall" in nineteenth century English Literature. The name "Mur des Lamentations" was used in French and "Klagemauer" in German. The Arabs referred to the wall as the al-Buraq Wall. what is the significance of the mosque that is mentioned in the previous answer? It is the third holiest site in Islam.  Muslims believe that Muhammad was transported from the Great Mosque of Mecca to al-Aqsa during the Night Journey. where is it located? The Old City of Jerusalem
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Al-Aqsa Mosque [SEP] Construction by the Umayyads
The current construction of the al-Aqsa Mosque is dated to the early Umayyad period of rule in Palestine. Architectural historian K. A. C. Creswell, referring to a testimony by Arculf, a Gallic monk, during his pilgrimage to Palestine in 679–82, notes the possibility that the second caliph of the Rashidun Caliphate, Umar ibn al-Khattab, erected a primitive quadrangular building for a capacity of 3,000 worshipers somewhere on the Haram ash-Sharif. However, Arculf visited Palestine during the reign of Mu'awiyah I, and it is possible that Mu'awiyah ordered the construction, not Umar. This latter claim is explicitly supported by the early Muslim scholar al-Muthahhar bin Tahir.