please be more sepecific. As I understand here, A was supposed to commence with the construction and complete it and handover the duly completed construction to B?? if the above statement by me is correct, then please note, that the 'Act of God' and reasonable time due to delays of departments and other formalaties are permitted. ' Act of God' means that due to Nature and its devastating natural forces such as heavy rain, Landslide, earthquake, Tsunami, Avalanches etc one cannot claim under these circumstances.
Also, you have not mentioned that by how long the period is over due of 2 years..