// You'll have to handle balances yourself, lets assume you have them in an object like the one below which is an example.
var balances = {
	"cainy393"	: 0.7,
	"raoulbtc"	: 2.1,
	"admin"		: 1.2
};

function startANewRaffle(){
	var ticketsRemaining = 1000;
	var ticketPrice = 0.01; // In mBTC
	var prize = 10; // In mBTC
	var tickets = [];
	// Announce a new raffle has started and display the above variables.
}

function buyTickets(user, numberOfTickets){
	if(numberOfTickets <= ticketsRemaining && balances[user] >= ticketPrice * numberOfTickets){
		ticketsRemaining = ticketsRemaining - numberOfTickets;
		for(var i=0;i<numberOfTickets;i++){
			tickets.push(user);
			balances[user] = balances[user] - ticketPrice;
		}
		// Tell the user they have successfully bought their tickets and maybe state how may are left?
		// Now we need to check if the tickets are sold out.
		if(ticketsRemaining == 0){
			endRaffle();
		}
	}else{
		// Tell the user there aren't enough tickets left or that they haven't got enough money.
	}
}

function endRaffle(){
	var winner = tickets[(Math.random()*tickets.length).floor()]
	balances[user] = balances[user] + prize;
	// Announce the winner and their winnings.
	startANewRaffle();
}