Dear Raj
Before starting the work you should make written agreement with the contracor about payment shedule. One patteren is given below.
h) Proper receipt of every payment should be taken; if possible payment should be made through cheque.
There are lot of material about construction for knowledge on the web site gharexpert.com, where you can find about construction, vastu, interioretc. For hiring contractor and payment shedule see article link given below.