What i have heard, is as follows:

If you rent is below Qar 5000/-, they can increase it up with 5% annually, where as below Qar 10,000/-, they can increase it up with 10% annually. Anything above Qar 10,000 is subjected to a 15% increase annually. But looking at the current trend and also people talking about it... places that used to cost, Qar 7500/- (For 2-bedroom apartment)has now come down to Qar 5000/-