Hi Krinpit,
As far as i am aware, if you purchase the property as a FTB and you rent it out within the first years then you are treated as an investor and not a FTB therefore you will be liable for the stamp duty whatever the rate is at the time of purchase.
Can i ask why you want to rent it out? You could live in yourself and rent out the other room(s) and claim rent a room relief earning up to €7,620 in rental income without being taxed on it! Maybe that is not an option for you i don't really know.
Jockey