income from selling flats

I wanted to ask say if I help a builder selling his flats and say he pays me RS 40000 for every flat sold. from april 2017 to feb 2018 say i sold 8 flats....and I dont have any other income....now do I need to file return since he paid me in cash....and I want to deposit the money (8x40000= 3,20,000) plus 3 flats sold this year that is 1,20,000 in bank


now say for depositing 4,40,000 in bank...I need to show only 3.20 in it return right??
will I immediately get any notice or something from income tax about the remaining amount that is 1.20??

also what itr to file??

and do I need to take a writen memo from builder that he paid me this cash against selling flat???