With reference to your query, you will be eligible to claim exemptions under sections 54 and 54F of the Income-tax Act, 1961 as the construction of work has been promised to be completed by the builder by May 2016.
As per the definition of construction, i presume the builder has completed the following : (i.e slab work of your flat done, plastering of outer four side walls, plastering of internal room walls done, plastering of slab done, the property has a door affixed in the entrance, Access to property through stair case is complete etc.) . if these are complete, construction is also complete.
Just ensure that you have the possession of the property in some form or other. As pointed out by you that EB, Water , drainage etc are pending , you can also do a small house warming ceremony and take photo's of the same and keep it for records(ensure to have date and time stamp on it). House warming ceremony is a deemed possession. Even affixing a name board in the premises is deemed possession. .