Construction on roof top on builder flat

Issue legal notice through advocate,  asking to remove the construction.  Then file suit for mandatory injunction before civil court to demolish the toilet.

Generally these kind of matters are settled amicably after issuing legal notice itself.  Do not worry. 

Call or mail me for assistance. 

You are occupying first floor of the building whereas third (top) floor owner is stated to have constructed / added a "tiolet" on rooftop, does it affect your living / egress / ingress or title ?

Builder floors are rampant in Delhi, where neither provisions of Cooperative Societies Act nor Apartment Ownership Act nor Society Registration Act apply. 

Space in the roof is a common facility which is required to be utilised for common purpose. If there is Resident Welfare Association, you can take it up thru the said Association.