Promotional Giveaways

Hi. I wanted to find out what are the requirements I need to fulfill by law so as to start a promotional event wherein we giveaway 3 apartments to people who purchase an entry form and have an opportunity to win, for the sum of a small amount. Basically it is also in the form of promoting the company. And it may also come under a lottery scheme. Not too sure so I need some help in this area. I need to know if I hold this event for all residents of the state of goa. Will I be breaking any laws. Due to the fact I'll be having an open contest for people within the state of Goa. What type of company would i have to register. Do let me know ur thoughts if possible and also any legal ramifications if in any. Thank you.. Mr. Fernandes.